diff --git a/index.html b/index.html
index 0782aac..f805db5 100644
--- a/index.html
+++ b/index.html
@@ -24,6 +24,29 @@
   </head>
   <body>
     <div id="root"></div>
+    <script>
+      (function () {
+        var host = location.hostname;
+        if (host !== 'localhost' && host !== '127.0.0.1') return;
+        if (!navigator.serviceWorker) return;
+        var hadSw = false;
+        navigator.serviceWorker.getRegistrations().then(function (regs) {
+          hadSw = regs.length > 0;
+          return Promise.all(regs.map(function (r) { return r.unregister(); }));
+        }).then(function () {
+          if (!window.caches) return hadSw;
+          return caches.keys().then(function (keys) {
+            return Promise.all(keys.map(function (k) { return caches.delete(k); }))
+              .then(function () { return hadSw; });
+          });
+        }).then(function (reload) {
+          if (reload && !sessionStorage.getItem('dashfront-sw-cleared')) {
+            sessionStorage.setItem('dashfront-sw-cleared', '1');
+            location.reload();
+          }
+        });
+      })();
+    </script>
     <script type="module" src="/src/main.jsx"></script>
   </body>
 </html>
diff --git a/src/api/index.js b/src/api/index.js
index 6f1e4dd..a0a1fba 100644
--- a/src/api/index.js
+++ b/src/api/index.js
@@ -65,6 +65,8 @@ async function http(path, { method = 'GET', body } = {}) {
     logApi('error-body', { method, path, status: res.status, message, data });
     const err = new Error(message || `Request failed (${res.status})`);
     err.status = res.status;
+    err.path = path;
+    err.method = method;
     err.data = data;
     throw err;
   }
@@ -92,6 +94,30 @@ export const article = {
     const params = new URLSearchParams({ target });
     return http(`/api/article/get?${params}`);
   },
+
+  /**
+   * GET /api/article/byCategory?categoryId&offset&maxCount
+   * Articles assigned to a category (for tile view).
+   */
+  byCategory({ categoryId, offset, maxCount } = {}) {
+    const params = new URLSearchParams({ categoryId: String(categoryId) });
+    if (offset) params.set('offset', String(offset));
+    if (maxCount != null) params.set('maxCount', String(maxCount));
+    return http(`/api/article/byCategory?${params}`);
+  },
+};
+
+export const category = {
+  /**
+   * GET /api/category/tree?companyId=
+   * Flat map of categories keyed by id; rootCategoryId resolved server-side.
+   */
+  getTree({ companyId } = {}) {
+    const params = new URLSearchParams();
+    if (companyId != null) params.set('companyId', String(companyId));
+    const qs = params.toString();
+    return http(`/api/category/tree${qs ? `?${qs}` : ''}`);
+  },
 };
 
 export const company = {
@@ -119,14 +145,8 @@ export const company = {
   },
 
   /**
-   * Backend suggestion (not implemented yet):
-   *
    * PUT /api/company/:companyId
    * Body: { name, iso639, taxrate, reducedtaxrate }
-   * Response: { company: { id, name, iso639, taxrate, reducedtaxrate, ... } }
-   * Auth: session cookie; user must be allowed to edit that company.
-   *
-   * Optional: add iso639 to GET /api/company list items (today only languageId).
    */
   update(companyId, { name, iso639, taxrate, reducedtaxrate }) {
     return http(`/api/company/${companyId}`, {
@@ -194,4 +214,4 @@ export const auth = {
   },
 };
 
-export default { auth, article, company };
+export default { auth, article, category, company };
diff --git a/src/components/AuthBootstrap.jsx b/src/components/AuthBootstrap.jsx
index 88571b4..ad4834a 100644
--- a/src/components/AuthBootstrap.jsx
+++ b/src/components/AuthBootstrap.jsx
@@ -1,10 +1,15 @@
 import { Component } from 'react';
 import { connect } from 'react-redux';
 import { enqueueSnackbar } from 'notistack';
-import { bootstrapSession } from '../store/authSlice';
+import { bootstrapSession as bootstrapSessionThunk } from '../store/authSlice';
+
+let sessionBootstrapped = false;
 
 class AuthBootstrap extends Component {
   componentDidMount() {
+    if (sessionBootstrapped) return;
+    sessionBootstrapped = true;
+
     this.props
       .bootstrapSession()
       .unwrap()
@@ -24,7 +29,7 @@ class AuthBootstrap extends Component {
 }
 
 const mapDispatchToProps = (dispatch) => ({
-  bootstrapSession: () => dispatch(bootstrapSession()),
+  bootstrapSession: () => dispatch(bootstrapSessionThunk()),
 });
 
 export default connect(null, mapDispatchToProps)(AuthBootstrap);
diff --git a/src/components/BackendError.jsx b/src/components/BackendError.jsx
new file mode 100644
index 0000000..e1f6861
--- /dev/null
+++ b/src/components/BackendError.jsx
@@ -0,0 +1,55 @@
+import { Component } from 'react';
+import Alert from '@mui/material/Alert';
+import AlertTitle from '@mui/material/AlertTitle';
+import Box from '@mui/material/Box';
+import Button from '@mui/material/Button';
+import Typography from '@mui/material/Typography';
+import { formatBackendError } from '../utils/backendError';
+
+class BackendError extends Component {
+  render() {
+    const { error, title, onRetry, sx, action } = this.props;
+    if (!error) return null;
+
+    const formatted = formatBackendError(error);
+    const heading = title || formatted.title;
+
+    return (
+      <Alert
+        severity="error"
+        sx={{ maxWidth: 720, ...sx }}
+        action={action}
+      >
+        <AlertTitle>{heading}</AlertTitle>
+        {formatted.detail ? (
+          <Typography variant="body2" component="div" sx={{ mb: formatted.request ? 1 : 0 }}>
+            {formatted.detail}
+          </Typography>
+        ) : null}
+        {formatted.request ? (
+          <Box
+            component="code"
+            sx={{
+              display: 'block',
+              fontSize: '0.75rem',
+              color: 'text.secondary',
+              fontFamily: 'monospace',
+            }}
+          >
+            {formatted.request}
+            {formatted.status != null ? ` → ${formatted.status}` : ''}
+          </Box>
+        ) : null}
+        {onRetry ? (
+          <Box sx={{ mt: 1.5 }}>
+            <Button size="small" variant="outlined" color="inherit" onClick={onRetry}>
+              Erneut versuchen
+            </Button>
+          </Box>
+        ) : null}
+      </Alert>
+    );
+  }
+}
+
+export default BackendError;
diff --git a/src/components/CompanySettingsDialog.jsx b/src/components/CompanySettingsDialog.jsx
index 254e9e0..1ff38fb 100644
--- a/src/components/CompanySettingsDialog.jsx
+++ b/src/components/CompanySettingsDialog.jsx
@@ -16,19 +16,21 @@ import TextField from '@mui/material/TextField';
 import ToggleButton from '@mui/material/ToggleButton';
 import ToggleButtonGroup from '@mui/material/ToggleButtonGroup';
 import { enqueueSnackbar } from 'notistack';
-import { company } from '../api';
+import BackendError from './BackendError';
 import { selectAuthUser } from '../store/authSlice';
 import {
-  ISO639_OPTIONS,
-  companyLanguageToIso639,
-  parseTaxRate,
-} from '../utils/companyForm';
+  loadCurrentCompany,
+  selectCompanyStatus,
+  selectCurrentCompany,
+  updateCompany as updateCompanyThunk,
+} from '../store/companySlice';
+import { ISO639_OPTIONS, parseTaxRate } from '../utils/companyForm';
+import { backendErrorFrom, isBackendFailure } from '../utils/backendError';
 
 class CompanySettingsDialog extends Component {
   constructor(props) {
     super(props);
     this.state = {
-      loading: false,
       busy: false,
       error: null,
       name: '',
@@ -37,39 +39,37 @@ class CompanySettingsDialog extends Component {
       reducedtaxrate: '',
     };
     this.handleSubmit = this.handleSubmit.bind(this);
+    this.syncFormFromCompany = this.syncFormFromCompany.bind(this);
   }
 
   componentDidUpdate(prevProps) {
-    const { open, user } = this.props;
-    const companyId = user?.selectedCompanyId;
-    if (open && !prevProps.open && companyId) {
-      void this.loadCompany(companyId);
+    const { open, company, companyStatus } = this.props;
+    if (open && !prevProps.open) {
+      this.setState({ error: null });
+      if (company) {
+        this.syncFormFromCompany(company);
+      } else if (companyStatus !== 'loading') {
+        void this.props.loadCurrentCompany();
+      }
+    }
+    if (open && company && company !== prevProps.company) {
+      this.syncFormFromCompany(company);
     }
   }
 
-  async loadCompany(companyId) {
-    this.setState({ loading: true, error: null });
-    try {
-      const data = await company.getById(companyId);
-      const item = data.company;
-      this.setState({
-        name: item.name ?? '',
-        iso639: companyLanguageToIso639(item),
-        taxrate: item.taxrate != null ? String(item.taxrate) : '',
-        reducedtaxrate: item.reducedtaxrate != null ? String(item.reducedtaxrate) : '',
-      });
-    } catch (err) {
-      this.setState({ error: err.message });
-    } finally {
-      this.setState({ loading: false });
-    }
+  syncFormFromCompany(company) {
+    this.setState({
+      name: company.name ?? '',
+      iso639: company.iso639 ?? 'de',
+      taxrate: company.taxrate != null ? String(company.taxrate) : '',
+      reducedtaxrate: company.reducedtaxrate != null ? String(company.reducedtaxrate) : '',
+    });
   }
 
   async handleSubmit(event) {
     event.preventDefault();
-    const { user, onClose } = this.props;
+    const { onClose } = this.props;
     const { name, iso639, taxrate, reducedtaxrate } = this.state;
-    const companyId = user?.selectedCompanyId;
     const parsedTaxrate = parseTaxRate(taxrate);
     const parsedReducedtaxrate = parseTaxRate(reducedtaxrate);
     const canSave =
@@ -78,31 +78,34 @@ class CompanySettingsDialog extends Component {
       parsedTaxrate != null &&
       parsedReducedtaxrate != null;
 
-    if (!companyId || !canSave) {
+    if (!canSave) {
       this.setState({ error: 'Bitte alle Pflichtfelder ausfüllen.' });
       return;
     }
 
     this.setState({ busy: true, error: null });
     try {
-      await company.update(companyId, {
-        name: name.trim(),
-        iso639,
-        taxrate: parsedTaxrate,
-        reducedtaxrate: parsedReducedtaxrate,
-      });
+      await this.props
+        .updateCompany({
+          name: name.trim(),
+          iso639,
+          taxrate: parsedTaxrate,
+          reducedtaxrate: parsedReducedtaxrate,
+        })
+        .unwrap();
       enqueueSnackbar('Unternehmen gespeichert.', { variant: 'success' });
       onClose();
     } catch (err) {
-      this.setState({ error: err.message });
+      this.setState({ error: backendErrorFrom(err) });
     } finally {
       this.setState({ busy: false });
     }
   }
 
   render() {
-    const { open, onClose } = this.props;
-    const { loading, busy, error, name, iso639, taxrate, reducedtaxrate } = this.state;
+    const { open, onClose, companyStatus } = this.props;
+    const { busy, error, name, iso639, taxrate, reducedtaxrate } = this.state;
+    const loading = companyStatus === 'loading' && !busy;
     const parsedTaxrate = parseTaxRate(taxrate);
     const parsedReducedtaxrate = parseTaxRate(reducedtaxrate);
     const canSave =
@@ -117,9 +120,13 @@ class CompanySettingsDialog extends Component {
         <Box component="form" onSubmit={this.handleSubmit} noValidate>
           <DialogContent>
             {error ? (
-              <Alert severity="error" sx={{ mb: 2 }}>
-                {error}
-              </Alert>
+              isBackendFailure(error) ? (
+                <BackendError error={error} sx={{ mb: 2 }} />
+              ) : (
+                <Alert severity="error" sx={{ mb: 2 }}>
+                  {typeof error === 'string' ? error : error.message}
+                </Alert>
+              )
             ) : null}
 
             {loading ? (
@@ -212,6 +219,13 @@ class CompanySettingsDialog extends Component {
 
 const mapStateToProps = (state) => ({
   user: selectAuthUser(state),
+  company: selectCurrentCompany(state),
+  companyStatus: selectCompanyStatus(state),
 });
 
-export default connect(mapStateToProps)(CompanySettingsDialog);
+const mapDispatchToProps = (dispatch) => ({
+  loadCurrentCompany: () => dispatch(loadCurrentCompany()),
+  updateCompany: (payload) => dispatch(updateCompanyThunk(payload)),
+});
+
+export default connect(mapStateToProps, mapDispatchToProps)(CompanySettingsDialog);
diff --git a/src/components/CompanySetupDialog.jsx b/src/components/CompanySetupDialog.jsx
index e9a29ff..78e890a 100644
--- a/src/components/CompanySetupDialog.jsx
+++ b/src/components/CompanySetupDialog.jsx
@@ -20,13 +20,19 @@ import ToggleButton from '@mui/material/ToggleButton';
 import ToggleButtonGroup from '@mui/material/ToggleButtonGroup';
 import Typography from '@mui/material/Typography';
 import BusinessIcon from '@mui/icons-material/Business';
+import BackendError from './BackendError';
 import { company } from '../api';
-import { createCompany, logout, selectCompany } from '../store/authSlice';
+import {
+  createCompany as createCompanyThunk,
+  logout as logoutThunk,
+  selectCompany as selectCompanyThunk,
+} from '../store/authSlice';
 import {
   defaultIso639,
   ISO639_OPTIONS,
   parseTaxRate,
 } from '../utils/companyForm';
+import { backendErrorFrom, isBackendFailure } from '../utils/backendError';
 
 class CompanySetupDialog extends Component {
   constructor(props) {
@@ -44,6 +50,7 @@ class CompanySetupDialog extends Component {
     this.handleSelect = this.handleSelect.bind(this);
     this.handleCreate = this.handleCreate.bind(this);
     this.handleLogout = this.handleLogout.bind(this);
+    this.handleClose = this.handleClose.bind(this);
   }
 
   componentDidMount() {
@@ -67,7 +74,7 @@ class CompanySetupDialog extends Component {
     try {
       await this.props.selectCompany(companyId).unwrap();
     } catch (err) {
-      this.setState({ error: err.message });
+      this.setState({ error: backendErrorFrom(err) });
     } finally {
       this.setState({ busy: false });
     }
@@ -100,7 +107,7 @@ class CompanySetupDialog extends Component {
         })
         .unwrap();
     } catch (err) {
-      this.setState({ error: err.message });
+      this.setState({ error: backendErrorFrom(err) });
     } finally {
       this.setState({ busy: false });
     }
@@ -110,6 +117,10 @@ class CompanySetupDialog extends Component {
     void this.props.logout();
   }
 
+  handleClose(_event, reason) {
+    if (reason === 'backdropClick' || reason === 'escapeKeyDown') return;
+  }
+
   render() {
     const { companies, loading, busy, error, name, iso639, taxrate, reducedtaxrate } =
       this.state;
@@ -123,7 +134,7 @@ class CompanySetupDialog extends Component {
       parsedReducedtaxrate != null;
 
     return (
-      <Dialog open disableEscapeKeyDown maxWidth="sm" fullWidth>
+      <Dialog open onClose={this.handleClose} maxWidth="sm" fullWidth>
         <DialogTitle>
           {loading
             ? 'Unternehmen'
@@ -141,9 +152,13 @@ class CompanySetupDialog extends Component {
           ) : null}
 
           {error ? (
-            <Alert severity="error" sx={{ mb: 2 }}>
-              {error}
-            </Alert>
+            isBackendFailure(error) ? (
+              <BackendError error={error} sx={{ mb: 2 }} />
+            ) : (
+              <Alert severity="error" sx={{ mb: 2 }}>
+                {typeof error === 'string' ? error : error.message}
+              </Alert>
+            )
           ) : null}
 
           {loading ? (
@@ -268,9 +283,9 @@ class CompanySetupDialog extends Component {
 }
 
 const mapDispatchToProps = (dispatch) => ({
-  createCompany: (payload) => dispatch(createCompany(payload)),
-  selectCompany: (companyId) => dispatch(selectCompany(companyId)),
-  logout: () => dispatch(logout()),
+  createCompany: (payload) => dispatch(createCompanyThunk(payload)),
+  selectCompany: (companyId) => dispatch(selectCompanyThunk(companyId)),
+  logout: () => dispatch(logoutThunk()),
 });
 
 export default connect(null, mapDispatchToProps)(CompanySetupDialog);
diff --git a/src/components/tiles/ActionTile.jsx b/src/components/tiles/ActionTile.jsx
new file mode 100644
index 0000000..e2bd20d
--- /dev/null
+++ b/src/components/tiles/ActionTile.jsx
@@ -0,0 +1,18 @@
+import AddIcon from '@mui/icons-material/Add';
+import Typography from '@mui/material/Typography';
+import { Tile } from './Tile';
+
+export class ActionTile extends Tile {
+  renderIcon() {
+    return <AddIcon color="primary" sx={{ fontSize: 40 }} />;
+  }
+
+  renderLabel() {
+    const { label = 'Aktion' } = this.props;
+    return (
+      <Typography variant="body2" fontWeight={600} sx={{ lineHeight: 1.2 }}>
+        {label}
+      </Typography>
+    );
+  }
+}
diff --git a/src/components/tiles/ArticleTile.jsx b/src/components/tiles/ArticleTile.jsx
new file mode 100644
index 0000000..c8a95db
--- /dev/null
+++ b/src/components/tiles/ArticleTile.jsx
@@ -0,0 +1,27 @@
+import Inventory2OutlinedIcon from '@mui/icons-material/Inventory2Outlined';
+import Typography from '@mui/material/Typography';
+import { Tile } from './Tile';
+import { formatPrice } from '../../utils/price';
+
+export class ArticleTile extends Tile {
+  renderIcon() {
+    return <Inventory2OutlinedIcon color="action" sx={{ fontSize: 36 }} />;
+  }
+
+  renderSecondary() {
+    const { article } = this.props;
+    if (!article) return null;
+    return (
+      <>
+        <Typography variant="caption" color="text.secondary" noWrap sx={{ maxWidth: '100%' }}>
+          {article.sku}
+        </Typography>
+        {article.price != null && (
+          <Typography variant="caption" fontWeight={600}>
+            {formatPrice(article.price)}
+          </Typography>
+        )}
+      </>
+    );
+  }
+}
diff --git a/src/components/tiles/BackTile.jsx b/src/components/tiles/BackTile.jsx
new file mode 100644
index 0000000..1ed6eb7
--- /dev/null
+++ b/src/components/tiles/BackTile.jsx
@@ -0,0 +1,18 @@
+import ArrowBackIcon from '@mui/icons-material/ArrowBack';
+import Typography from '@mui/material/Typography';
+import { Tile } from './Tile';
+
+export class BackTile extends Tile {
+  renderIcon() {
+    return <ArrowBackIcon color="action" sx={{ fontSize: 36 }} />;
+  }
+
+  renderLabel() {
+    const { label = 'Zurück' } = this.props;
+    return (
+      <Typography variant="body2" fontWeight={600} sx={{ lineHeight: 1.2 }}>
+        {label}
+      </Typography>
+    );
+  }
+}
diff --git a/src/components/tiles/CategoryTile.jsx b/src/components/tiles/CategoryTile.jsx
new file mode 100644
index 0000000..1910197
--- /dev/null
+++ b/src/components/tiles/CategoryTile.jsx
@@ -0,0 +1,8 @@
+import FolderIcon from '@mui/icons-material/Folder';
+import { Tile } from './Tile';
+
+export class CategoryTile extends Tile {
+  renderIcon() {
+    return <FolderIcon color="primary" sx={{ fontSize: 40 }} />;
+  }
+}
diff --git a/src/components/tiles/Tile.jsx b/src/components/tiles/Tile.jsx
new file mode 100644
index 0000000..60c9dc3
--- /dev/null
+++ b/src/components/tiles/Tile.jsx
@@ -0,0 +1,81 @@
+import { Component } from 'react';
+import Paper from '@mui/material/Paper';
+import Typography from '@mui/material/Typography';
+
+export const TILE_SIZE = 140;
+
+export const tileBaseSx = {
+  aspectRatio: '1 / 1',
+  width: '100%',
+  display: 'flex',
+  flexDirection: 'column',
+  alignItems: 'center',
+  justifyContent: 'center',
+  gap: 1,
+  p: 1.5,
+  cursor: 'pointer',
+  userSelect: 'none',
+  textAlign: 'center',
+  transition: 'border-color 0.15s, background-color 0.15s',
+  '&:hover': {
+    bgcolor: 'action.hover',
+    borderColor: 'primary.main',
+  },
+};
+
+export class Tile extends Component {
+  handleClick = () => {
+    this.props.onClick?.();
+  };
+
+  renderIcon() {
+    return null;
+  }
+
+  renderLabel() {
+    const { label } = this.props;
+    if (!label) return null;
+    return (
+      <Typography variant="body2" fontWeight={600} sx={{ lineHeight: 1.2 }}>
+        {label}
+      </Typography>
+    );
+  }
+
+  renderSecondary() {
+    const { secondary } = this.props;
+    if (!secondary) return null;
+    return (
+      <Typography variant="caption" color="text.secondary" sx={{ lineHeight: 1.2 }}>
+        {secondary}
+      </Typography>
+    );
+  }
+
+  render() {
+    const { sx, disabled } = this.props;
+    return (
+      <Paper
+        variant="outlined"
+        component="button"
+        type="button"
+        disabled={disabled}
+        onClick={this.handleClick}
+        sx={{
+          ...tileBaseSx,
+          border: '1px solid',
+          borderColor: 'divider',
+          bgcolor: 'background.paper',
+          ...(disabled
+            ? { opacity: 0.5, pointerEvents: 'none' }
+            : {}),
+          ...sx,
+        }}
+      >
+        {this.renderIcon()}
+        {this.renderLabel()}
+        {this.renderSecondary()}
+      </Paper>
+    );
+  }
+}
diff --git a/src/components/tiles/index.js b/src/components/tiles/index.js
new file mode 100644
index 0000000..fb452d6
--- /dev/null
+++ b/src/components/tiles/index.js
@@ -0,0 +1,5 @@
+export { TILE_SIZE, Tile, tileBaseSx } from './Tile';
+export { BackTile } from './BackTile';
+export { CategoryTile } from './CategoryTile';
+export { ArticleTile } from './ArticleTile';
+export { ActionTile } from './ActionTile';
diff --git a/src/components/withNavigate.jsx b/src/components/withNavigate.jsx
new file mode 100644
index 0000000..4b0354b
--- /dev/null
+++ b/src/components/withNavigate.jsx
@@ -0,0 +1,9 @@
+import { useNavigate } from 'react-router-dom';
+
+export default function withNavigate(Wrapped) {
+  function NavigateWrapper(props) {
+    const navigate = useNavigate();
+    return <Wrapped {...props} navigate={navigate} />;
+  }
+  return NavigateWrapper;
+}
diff --git a/src/main.jsx b/src/main.jsx
index ee701dc..e42040e 100644
--- a/src/main.jsx
+++ b/src/main.jsx
@@ -3,14 +3,25 @@ import CssBaseline from '@mui/material/CssBaseline';
 import { ThemeProvider } from '@mui/material/styles';
 import { Provider } from 'react-redux';
 import { SnackbarProvider } from 'notistack';
-import { registerSW } from 'virtual:pwa-register';
 import AuthBootstrap from './components/AuthBootstrap';
 import App from './App';
 import { store } from './store';
 import theme from './theme';
 import './index.css';
 
-registerSW({ immediate: true });
+async function clearDevServiceWorker() {
+  if (!import.meta.env.DEV || !('serviceWorker' in navigator)) return;
+  const regs = await navigator.serviceWorker.getRegistrations();
+  await Promise.all(regs.map((r) => r.unregister()));
+  if ('caches' in window) {
+    const keys = await caches.keys();
+    await Promise.all(keys.map((k) => caches.delete(k)));
+  }
+}
+
+if (import.meta.env.DEV) {
+  void clearDevServiceWorker();
+}
 
 createRoot(document.getElementById('root')).render(
   <Provider store={store}>
diff --git a/src/pages/artikel/index.jsx b/src/pages/artikel/index.jsx
index e0b0573..ac4f5bb 100644
--- a/src/pages/artikel/index.jsx
+++ b/src/pages/artikel/index.jsx
@@ -1,5 +1,4 @@
 import { Component } from 'react';
-import Alert from '@mui/material/Alert';
 import Box from '@mui/material/Box';
 import InputAdornment from '@mui/material/InputAdornment';
 import List from '@mui/material/List';
@@ -11,6 +10,8 @@ import Typography from '@mui/material/Typography';
 import SearchIcon from '@mui/icons-material/Search';
 import ClearIcon from '@mui/icons-material/Clear';
 import { article } from '../../api';
+import BackendError from '../../components/BackendError';
+import { backendErrorFrom } from '../../utils/backendError';
 import { formatPrice } from '../../utils/price';
 import {
   buildSearchUrl,
@@ -273,7 +274,7 @@ class ArtikelSearchPage extends Component {
         categoryFacets: null,
         totalCount: null,
         recordset: null,
-        error: err.message || 'Suche fehlgeschlagen',
+        error: backendErrorFrom(err),
       });
     }
   };
@@ -344,9 +345,11 @@ class ArtikelSearchPage extends Component {
         )}
 
         {error && (
-          <Alert severity="error" sx={{ mb: 2 }}>
-            {error}
-          </Alert>
+          <BackendError
+            error={error}
+            sx={{ mb: 2 }}
+            onRetry={this.fetchResults}
+          />
         )}
 
         {searchActive && (
diff --git a/src/pages/artikel/kategorien.jsx b/src/pages/artikel/kategorien.jsx
index 42487e2..63e7d4f 100644
--- a/src/pages/artikel/kategorien.jsx
+++ b/src/pages/artikel/kategorien.jsx
@@ -1,7 +1,227 @@
+import { Component } from 'react';
+import { connect } from 'react-redux';
+import Box from '@mui/material/Box';
+import CircularProgress from '@mui/material/CircularProgress';
 import Typography from '@mui/material/Typography';
+import BackendError from '../../components/BackendError';
+import {
+  ActionTile,
+  ArticleTile,
+  BackTile,
+  CategoryTile,
+  TILE_SIZE,
+} from '../../components/tiles';
+import withNavigate from '../../components/withNavigate';
+import { selectCompanyId } from '../../store/companySlice';
+import {
+  categoryDisplayName,
+  loadCategoryArticles,
+  loadCategoryTree,
+  navigateBack,
+  navigateToCategory,
+  selectCanNavigateBack,
+  selectCategoryArticles,
+  selectCategoryArticlesStatus,
+  selectCategoryError,
+  selectCategoryTreeStatus,
+  selectChildCategories,
+  selectCurrentCategory,
+} from '../../store/categorySlice';
 
-export default function ArtikelKategorienPage() {
-  return (
-    <Typography color="text.secondary">Kategorien — Inhalt folgt.</Typography>
-  );
+const gridSx = {
+  display: 'grid',
+  gridTemplateColumns: `repeat(auto-fill, minmax(${TILE_SIZE}px, 1fr))`,
+  gap: 2,
+};
+
+class ArtikelKategorienPage extends Component {
+  componentDidMount() {
+    this.ensureTreeLoaded();
+    this.ensureArticlesLoaded();
+  }
+
+  componentDidUpdate(prevProps) {
+    if (this.props.companyId !== prevProps.companyId) {
+      this.ensureTreeLoaded();
+    }
+    if (this.props.currentCategoryId !== prevProps.currentCategoryId) {
+      this.ensureArticlesLoaded();
+    }
+    if (
+      this.props.treeStatus === 'succeeded' &&
+      prevProps.treeStatus !== 'succeeded'
+    ) {
+      this.ensureArticlesLoaded();
+    }
+  }
+
+  ensureTreeLoaded = () => {
+    const { companyId, treeStatus } = this.props;
+    if (!companyId || treeStatus !== 'idle') return;
+    this.props.loadCategoryTree(companyId);
+  };
+
+  ensureArticlesLoaded = () => {
+    const { currentCategoryId, articlesStatus, rootCategoryId } = this.props;
+    if (!currentCategoryId || articlesStatus !== 'idle') return;
+    // Root articles come from tree response; only fetch for subcategories.
+    if (String(currentCategoryId) === String(rootCategoryId)) return;
+    this.props.loadCategoryArticles({ categoryId: currentCategoryId });
+  };
+
+  handleRetryTree = () => {
+    const { companyId } = this.props;
+    if (companyId) this.props.loadCategoryTree(companyId);
+  };
+
+  handleRetryArticles = () => {
+    const { currentCategoryId } = this.props;
+    if (currentCategoryId) {
+      this.props.loadCategoryArticles({ categoryId: currentCategoryId });
+    }
+  };
+
+  handleCategoryClick = (categoryId) => {
+    this.props.navigateToCategory(categoryId);
+  };
+
+  handleArticleClick = (sku) => {
+    this.props.navigate(`/artikel/${encodeURIComponent(sku)}`);
+  };
+
+  render() {
+    const {
+      companyId,
+      rootCategoryId,
+      treeStatus,
+      articlesStatus,
+      error,
+      canGoBack,
+      currentCategory,
+      currentCategoryId,
+      childCategories,
+      articles,
+    } = this.props;
+
+    if (!companyId) {
+      return (
+        <Typography color="text.secondary">
+          Kein Unternehmen ausgewählt.
+        </Typography>
+      );
+    }
+
+    if (treeStatus === 'loading' || treeStatus === 'idle') {
+      return (
+        <Box sx={{ display: 'flex', justifyContent: 'center', py: 6 }}>
+          <CircularProgress />
+        </Box>
+      );
+    }
+
+    if (treeStatus === 'failed') {
+      return (
+        <BackendError
+          error={error}
+          onRetry={this.handleRetryTree}
+        />
+      );
+    }
+
+    if (!rootCategoryId) {
+      return (
+        <Typography color="text.secondary">
+          Kategoriebaum ist leer.
+        </Typography>
+      );
+    }
+
+    const categoryName = categoryDisplayName(
+      currentCategory?.name,
+      currentCategoryId,
+      rootCategoryId,
+    );
+    const showArticlesLoading = articlesStatus === 'loading';
+
+    return (
+      <>
+        {categoryName ? (
+          <Typography variant="subtitle1" sx={{ mb: 2, fontWeight: 600 }}>
+            {categoryName}
+          </Typography>
+        ) : null}
+
+        {error && articlesStatus === 'failed' && (
+          <BackendError
+            error={error}
+            sx={{ mb: 2 }}
+            onRetry={this.handleRetryArticles}
+          />
+        )}
+
+        <Box sx={gridSx}>
+          {canGoBack && (
+            <BackTile onClick={this.props.navigateBack} />
+          )}
+
+          {childCategories.map((item) => (
+            <CategoryTile
+              key={item.id}
+              label={categoryDisplayName(item.name, item.id, rootCategoryId)}
+              onClick={() => this.handleCategoryClick(item.id)}
+            />
+          ))}
+
+          {articles.map((item) => (
+            <ArticleTile
+              key={item.id ?? item.sku}
+              label={item.name?.trim() || undefined}
+              article={item}
+              onClick={() => this.handleArticleClick(item.sku)}
+            />
+          ))}
+
+          <ActionTile
+            label="Neue Kategorie"
+            disabled
+            onClick={() => {}}
+          />
+          <ActionTile
+            label="Neuer Artikel"
+            disabled
+            onClick={() => {}}
+          />
+        </Box>
+
+        {showArticlesLoading && (
+          <Box sx={{ display: 'flex', justifyContent: 'center', py: 4 }}>
+            <CircularProgress size={28} />
+          </Box>
+        )}
+
+      </>
+    );
+  }
 }
+
+const mapStateToProps = (state) => ({
+  companyId: selectCompanyId(state),
+  rootCategoryId: state.category.rootCategoryId,
+  treeStatus: selectCategoryTreeStatus(state),
+  articlesStatus: selectCategoryArticlesStatus(state),
+  error: selectCategoryError(state),
+  currentCategoryId: state.category.currentCategoryId,
+  currentCategory: selectCurrentCategory(state),
+  childCategories: selectChildCategories(state),
+  articles: selectCategoryArticles(state),
+  canGoBack: selectCanNavigateBack(state),
+});
+
+const mapDispatchToProps = {
+  loadCategoryTree,
+  loadCategoryArticles,
+  navigateToCategory,
+  navigateBack,
+};
+
+export default withNavigate(connect(mapStateToProps, mapDispatchToProps)(ArtikelKategorienPage));
diff --git a/src/pages/artikel/sku.jsx b/src/pages/artikel/sku.jsx
index 3bcd472..8f1ce27 100644
--- a/src/pages/artikel/sku.jsx
+++ b/src/pages/artikel/sku.jsx
@@ -1,4 +1,4 @@
-import { useEffect, useState } from 'react';
+import { useCallback, useEffect, useState } from 'react';
 import { Link as RouterLink, useNavigate, useParams } from 'react-router-dom';
 import Alert from '@mui/material/Alert';
 import Box from '@mui/material/Box';
@@ -13,6 +13,8 @@ import TableHead from '@mui/material/TableHead';
 import TableRow from '@mui/material/TableRow';
 import Typography from '@mui/material/Typography';
 import { article } from '../../api';
+import BackendError from '../../components/BackendError';
+import { backendErrorFrom, isBackendFailure } from '../../utils/backendError';
 import { formatPrice, getBrutto } from '../../utils/price';
 import { formatStock } from './searchFormat';
 
@@ -272,6 +274,11 @@ export default function ArtikelSkuPage() {
   const [data, setData] = useState(null);
   const [error, setError] = useState(null);
   const [loading, setLoading] = useState(true);
+  const [reloadKey, setReloadKey] = useState(0);
+
+  const retry = useCallback(() => {
+    setReloadKey((key) => key + 1);
+  }, []);
 
   useEffect(() => {
     function onKeyDown(e) {
@@ -306,7 +313,7 @@ export default function ArtikelSkuPage() {
       } catch (err) {
         if (!cancelled) {
           setData(null);
-          setError(err.message || 'Artikel konnte nicht geladen werden');
+          setError(backendErrorFrom(err));
         }
       } finally {
         if (!cancelled) setLoading(false);
@@ -317,7 +324,7 @@ export default function ArtikelSkuPage() {
     return () => {
       cancelled = true;
     };
-  }, [target]);
+  }, [target, reloadKey]);
 
   if (loading) {
     return (
@@ -328,9 +335,17 @@ export default function ArtikelSkuPage() {
   }
 
   if (error) {
+    if (isBackendFailure(error)) {
+      return (
+        <BackendError
+          error={error}
+          onRetry={retry}
+        />
+      );
+    }
     return (
       <Alert severity="error" sx={{ maxWidth: 640 }}>
-        {error}
+        {typeof error === 'string' ? error : error.message}
       </Alert>
     );
   }
diff --git a/src/store/authSlice.js b/src/store/authSlice.js
index a7d65fe..1b2d668 100644
--- a/src/store/authSlice.js
+++ b/src/store/authSlice.js
@@ -31,11 +31,17 @@ export const logout = createAsyncThunk('auth/logout', async () => {
   window.history.replaceState(null, '', '/');
 });
 
+function mergeUser(state, incoming) {
+  if (!incoming) return state.user;
+  const selectedCompanyId =
+    incoming.selectedCompanyId ?? state.user?.selectedCompanyId ?? null;
+  return { ...state.user, ...incoming, selectedCompanyId };
+}
+
 const initialState = {
   user: null,
   googleClientId: null,
   status: 'loading',
-  companyReady: false,
 };
 
 const authSlice = createSlice({
@@ -46,40 +52,47 @@ const authSlice = createSlice({
     builder
       .addCase(bootstrapSession.fulfilled, (state, action) => {
         const session = action.payload;
-        state.user = session.user ?? null;
-        state.googleClientId = session.googleClientId ?? null;
-        state.status = session.user ? 'authed' : 'anon';
-        state.companyReady = session.user?.selectedCompanyId != null;
+        state.googleClientId = session.googleClientId ?? state.googleClientId;
+        if (!session.user) {
+          if (state.status !== 'authed') {
+            state.user = null;
+            state.status = 'anon';
+          }
+          return;
+        }
+        state.user = mergeUser(state, session.user);
+        state.status = 'authed';
       })
       .addCase(bootstrapSession.rejected, (state) => {
-        state.user = null;
-        state.status = 'anon';
-        state.companyReady = false;
+        if (state.status === 'loading') {
+          state.user = null;
+          state.status = 'anon';
+        }
       })
       .addCase(loginWithGoogle.fulfilled, (state, action) => {
         const session = action.payload;
         state.user = session.user;
         state.googleClientId = session.googleClientId ?? state.googleClientId;
         state.status = 'authed';
-        state.companyReady = session.user?.selectedCompanyId != null;
       })
       .addCase(loginWithGoogle.rejected, (state) => {
         state.user = null;
         state.status = 'anon';
-        state.companyReady = false;
       })
       .addCase(selectCompany.fulfilled, (state, action) => {
-        state.user = { ...state.user, ...action.payload };
-        state.companyReady = true;
+        state.user = mergeUser(state, action.payload);
+        state.status = 'authed';
       })
       .addCase(createCompany.fulfilled, (state, action) => {
-        state.user = { ...state.user, ...action.payload };
-        state.companyReady = true;
+        state.user = mergeUser(state, action.payload);
+        state.status = 'authed';
+      })
+      .addCase(createCompany.rejected, (state, action) => {
+        console.error('[redux] createCompany.rejected', action.error?.message, action.payload);
       })
       .addCase(logout.fulfilled, (state) => {
         state.user = null;
         state.status = 'anon';
-        state.companyReady = false;
       });
   },
 });
@@ -88,6 +101,6 @@ export const selectAuthStatus = (state) => state.auth.status;
 export const selectAuthUser = (state) => state.auth.user;
 export const selectGoogleClientId = (state) => state.auth.googleClientId;
 export const selectNeedsCompanySetup = (state) =>
-  state.auth.status === 'authed' && !state.auth.companyReady;
+  state.auth.status === 'authed' && state.auth.user?.selectedCompanyId == null;
 
 export default authSlice.reducer;
diff --git a/src/store/categorySlice.js b/src/store/categorySlice.js
new file mode 100644
index 0000000..a2fd399
--- /dev/null
+++ b/src/store/categorySlice.js
@@ -0,0 +1,217 @@
+import { createAsyncThunk, createSlice } from '@reduxjs/toolkit';
+import { article, category } from '../api';
+import { catchBackendError, resolveBackendError } from '../utils/backendError';
+import { logout } from './authSlice';
+import { loadCurrentCompany } from './companySlice';
+
+export const ROOT_CATEGORY_NAME = 'Home';
+
+export function normalizeCategoryNode(item) {
+  return {
+    ...item,
+    id: item.id,
+    parentId: item.parentId ?? 0,
+    name: item.name?.trim() || null,
+  };
+}
+
+/** Backend: { tree: { tree: [...], articles: [] } } */
+export function parseCategoryTreeResponse(data, companyRootCategoryId = null) {
+  const payload = data?.tree ?? data;
+  const rawNodes = payload?.tree ?? payload?.categories ?? data?.categories ?? [];
+  const list = Array.isArray(rawNodes) ? rawNodes : Object.values(rawNodes);
+
+  const categories = Object.fromEntries(
+    list.map((item) => [String(item.id), normalizeCategoryNode(item)]),
+  );
+
+  const rootCategoryId = data?.rootCategoryId ?? companyRootCategoryId ?? null;
+  const rootArticles = Array.isArray(payload?.articles) ? payload.articles : [];
+
+  return { rootCategoryId, categories, rootArticles };
+}
+
+export function categoryDisplayName(name, categoryId, rootCategoryId) {
+  if (rootCategoryId != null && String(categoryId) === String(rootCategoryId)) {
+    return ROOT_CATEGORY_NAME;
+  }
+  return name?.trim() || '';
+}
+
+export function normalizeCategoryMap(data) {
+  return parseCategoryTreeResponse(data).categories;
+}
+
+export function getCategoryChildren(categories, parentId) {
+  if (!categories) return [];
+  const parentKey = String(parentId);
+  return Object.values(categories)
+    .filter((item) => String(item.parentId ?? 0) === parentKey)
+    .sort((a, b) => (a.sort ?? 0) - (b.sort ?? 0) || a.id - b.id);
+}
+
+export const loadCategoryTree = createAsyncThunk(
+  'category/loadTree',
+  async (companyId, { rejectWithValue, getState }) => {
+    try {
+      const data = await category.getTree({ companyId });
+      const fallbackRootId = getState().company.current?.rootCategoryId ?? null;
+      const { rootCategoryId, categories, rootArticles } = parseCategoryTreeResponse(
+        data,
+        fallbackRootId,
+      );
+      return {
+        companyId,
+        rootCategoryId,
+        categories,
+        rootArticles,
+      };
+    } catch (err) {
+      return catchBackendError(rejectWithValue)(err);
+    }
+  },
+);
+
+export const loadCategoryArticles = createAsyncThunk(
+  'category/loadArticles',
+  async ({ categoryId, offset = 0, maxCount = 200 } = {}, { rejectWithValue }) => {
+    try {
+      const data = await article.byCategory({ categoryId, offset, maxCount });
+      return {
+        categoryId,
+        recordset: data.recordset ?? [],
+        length: data.length ?? data.recordset?.length ?? 0,
+      };
+    } catch (err) {
+      return catchBackendError(rejectWithValue)(err);
+    }
+  },
+);
+
+const initialState = {
+  companyId: null,
+  categories: null,
+  rootCategoryId: null,
+  rootArticles: [],
+  currentCategoryId: null,
+  articles: [],
+  articlesTotal: 0,
+  treeStatus: 'idle',
+  articlesStatus: 'idle',
+  error: null,
+};
+
+const categorySlice = createSlice({
+  name: 'category',
+  initialState,
+  reducers: {
+    navigateToCategory(state, action) {
+      state.currentCategoryId = action.payload;
+      state.articles = [];
+      state.articlesTotal = 0;
+      state.articlesStatus = 'idle';
+      state.error = null;
+    },
+    navigateBack(state) {
+      const current = state.categories?.[String(state.currentCategoryId)];
+      const parentId = current?.parentId;
+      if (parentId == null || parentId === 0) return;
+      if (String(parentId) === String(state.rootCategoryId) || state.categories?.[String(parentId)]) {
+        state.currentCategoryId = parentId;
+        state.error = null;
+        if (String(parentId) === String(state.rootCategoryId)) {
+          state.articles = state.rootArticles;
+          state.articlesTotal = state.rootArticles.length;
+          state.articlesStatus = 'succeeded';
+        } else {
+          state.articles = [];
+          state.articlesTotal = 0;
+          state.articlesStatus = 'idle';
+        }
+      }
+    },
+    resetCategoryState() {
+      return initialState;
+    },
+  },
+  extraReducers: (builder) => {
+    builder
+      .addCase(loadCategoryTree.pending, (state) => {
+        state.treeStatus = 'loading';
+        state.error = null;
+      })
+      .addCase(loadCategoryTree.fulfilled, (state, action) => {
+        state.treeStatus = 'succeeded';
+        state.companyId = action.payload.companyId;
+        state.categories = action.payload.categories;
+        state.rootCategoryId = action.payload.rootCategoryId;
+        state.currentCategoryId = action.payload.rootCategoryId;
+        state.rootArticles = action.payload.rootArticles ?? [];
+        state.articles = state.rootArticles;
+        state.articlesTotal = state.rootArticles.length;
+        state.articlesStatus = 'succeeded';
+      })
+      .addCase(loadCategoryTree.rejected, (state, action) => {
+        state.treeStatus = 'failed';
+        state.error = resolveBackendError(action);
+      })
+      .addCase(loadCategoryArticles.pending, (state) => {
+        state.articlesStatus = 'loading';
+        state.error = null;
+      })
+      .addCase(loadCategoryArticles.fulfilled, (state, action) => {
+        state.articlesStatus = 'succeeded';
+        state.articles = action.payload.recordset;
+        state.articlesTotal = action.payload.length;
+      })
+      .addCase(loadCategoryArticles.rejected, (state, action) => {
+        state.articlesStatus = 'failed';
+        state.articles = [];
+        state.articlesTotal = 0;
+        state.error = resolveBackendError(action);
+      })
+      .addCase(loadCurrentCompany.fulfilled, (state, action) => {
+        const nextCompanyId = action.payload?.id ?? null;
+        if (nextCompanyId != null && nextCompanyId !== state.companyId) {
+          return {
+            ...initialState,
+            companyId: nextCompanyId,
+          };
+        }
+      })
+      .addCase(logout.fulfilled, () => initialState);
+  },
+});
+
+export const {
+  navigateToCategory,
+  navigateBack,
+  resetCategoryState,
+} = categorySlice.actions;
+
+export const selectCategoryMap = (state) => state.category.categories;
+export const selectCurrentCategoryId = (state) => state.category.currentCategoryId;
+export const selectCategoryRootId = (state) => state.category.rootCategoryId;
+export const selectCategoryTreeStatus = (state) => state.category.treeStatus;
+export const selectCategoryArticles = (state) => state.category.articles;
+export const selectCategoryArticlesStatus = (state) => state.category.articlesStatus;
+export const selectCategoryError = (state) => state.category.error;
+
+export const selectCurrentCategory = (state) => {
+  const id = state.category.currentCategoryId;
+  if (id == null) return null;
+  return state.category.categories?.[String(id)] ?? null;
+};
+
+export const selectChildCategories = (state) =>
+  getCategoryChildren(state.category.categories, state.category.currentCategoryId);
+
+export const selectCanNavigateBack = (state) => {
+  const { currentCategoryId, rootCategoryId, categories } = state.category;
+  if (currentCategoryId == null || rootCategoryId == null) return false;
+  if (String(currentCategoryId) === String(rootCategoryId)) return false;
+  const parentId = categories?.[String(currentCategoryId)]?.parentId;
+  return parentId != null && parentId !== 0;
+};
+
+export default categorySlice.reducer;
diff --git a/src/store/companySlice.js b/src/store/companySlice.js
new file mode 100644
index 0000000..a9578d2
--- /dev/null
+++ b/src/store/companySlice.js
@@ -0,0 +1,103 @@
+import { createAsyncThunk, createSlice } from '@reduxjs/toolkit';
+import { company } from '../api';
+import { normalizeCompany } from '../utils/companyForm';
+import {
+  bootstrapSession,
+  createCompany,
+  loginWithGoogle,
+  logout,
+  selectCompany,
+} from './authSlice';
+
+export const loadCurrentCompany = createAsyncThunk(
+  'company/loadCurrent',
+  async (_, { getState }) => {
+    const companyId = getState().auth.user?.selectedCompanyId;
+    if (!companyId) return null;
+    const data = await company.getById(companyId);
+    return normalizeCompany(data.company);
+  },
+);
+
+export const updateCompany = createAsyncThunk(
+  'company/update',
+  async (payload, { getState }) => {
+    const companyId = getState().auth.user?.selectedCompanyId;
+    if (!companyId) throw new Error('Kein Unternehmen ausgewählt.');
+    await company.update(companyId, payload);
+    const data = await company.getById(companyId);
+    return normalizeCompany(data.company, payload);
+  },
+);
+
+const initialState = {
+  current: null,
+  status: 'idle',
+  error: null,
+};
+
+const companySlice = createSlice({
+  name: 'company',
+  initialState,
+  reducers: {},
+  extraReducers: (builder) => {
+    builder
+      .addCase(loadCurrentCompany.pending, (state) => {
+        state.status = 'loading';
+        state.error = null;
+      })
+      .addCase(loadCurrentCompany.fulfilled, (state, action) => {
+        state.status = 'succeeded';
+        state.current = action.payload;
+      })
+      .addCase(loadCurrentCompany.rejected, (state, action) => {
+        state.status = 'failed';
+        state.error = action.error.message;
+      })
+      .addCase(updateCompany.pending, (state) => {
+        state.status = 'loading';
+        state.error = null;
+      })
+      .addCase(updateCompany.fulfilled, (state, action) => {
+        state.status = 'succeeded';
+        state.current = action.payload;
+      })
+      .addCase(updateCompany.rejected, (state, action) => {
+        state.status = 'failed';
+        state.error = action.error.message;
+      })
+      .addCase(logout.fulfilled, (state) => {
+        state.current = null;
+        state.status = 'idle';
+        state.error = null;
+      });
+  },
+});
+
+export const selectCurrentCompany = (state) => state.company.current;
+export const selectCompanyId = (state) => state.company.current?.id ?? null;
+export const selectCompanyStatus = (state) => state.company.status;
+export const selectCompanyError = (state) => state.company.error;
+export const selectCompanyName = (state) => state.company.current?.name ?? '';
+export const selectCompanyIso639 = (state) => state.company.current?.iso639 ?? 'de';
+export const selectCompanyTaxrate = (state) => state.company.current?.taxrate ?? null;
+export const selectCompanyReducedTaxrate = (state) => state.company.current?.reducedtaxrate ?? null;
+export const selectCompanyRootCategoryId = (state) => state.company.current?.rootCategoryId ?? null;
+
+export function companyLoadListener(listenerMiddleware) {
+  listenerMiddleware.startListening({
+    matcher: (action) =>
+      bootstrapSession.fulfilled.match(action) ||
+      loginWithGoogle.fulfilled.match(action) ||
+      selectCompany.fulfilled.match(action) ||
+      createCompany.fulfilled.match(action),
+    effect: async (_action, api) => {
+      const companyId = api.getState().auth.user?.selectedCompanyId;
+      if (companyId) {
+        api.dispatch(loadCurrentCompany());
+      }
+    },
+  });
+}
+
+export default companySlice.reducer;
diff --git a/src/store/index.js b/src/store/index.js
index e7b1251..85813d6 100644
--- a/src/store/index.js
+++ b/src/store/index.js
@@ -1,8 +1,45 @@
-import { configureStore } from '@reduxjs/toolkit';
+import { configureStore, createListenerMiddleware } from '@reduxjs/toolkit';
 import authReducer from './authSlice';
+import categoryReducer from './categorySlice';
+import companyReducer, { companyLoadListener } from './companySlice';
+
+const listenerMiddleware = createListenerMiddleware();
+companyLoadListener(listenerMiddleware);
+
+function reduxDevLogger() {
+  return (storeApi) => (next) => (action) => {
+    if (
+      !import.meta.env.DEV ||
+      (!action.type?.startsWith('auth/') &&
+        !action.type?.startsWith('company/') &&
+        !action.type?.startsWith('category/'))
+    ) {
+      return next(action);
+    }
+    const before = storeApi.getState();
+    const result = next(action);
+    const after = storeApi.getState();
+    console.log('[redux]', action.type, {
+      payload: action.payload,
+      auth: {
+        selectedCompanyId: after.auth.user?.selectedCompanyId ?? null,
+        needsCompanySetup:
+          after.auth.status === 'authed' && after.auth.user?.selectedCompanyId == null,
+      },
+      company: after.company.current,
+    });
+    return result;
+  };
+}
 
 export const store = configureStore({
   reducer: {
     auth: authReducer,
+    company: companyReducer,
+    category: categoryReducer,
   },
+  middleware: (getDefaultMiddleware) =>
+    getDefaultMiddleware()
+      .concat(listenerMiddleware.middleware)
+      .concat(import.meta.env.DEV ? reduxDevLogger() : []),
 });
diff --git a/src/utils/backendError.js b/src/utils/backendError.js
new file mode 100644
index 0000000..55acc27
--- /dev/null
+++ b/src/utils/backendError.js
@@ -0,0 +1,86 @@
+const STATUS_TITLES = {
+  400: 'Ungültige Anfrage',
+  401: 'Nicht angemeldet',
+  403: 'Zugriff verweigert',
+  404: 'Nicht gefunden',
+  409: 'Konflikt',
+  422: 'Ungültige Daten',
+  500: 'Serverfehler',
+  502: 'Gateway-Fehler',
+  503: 'Dienst nicht erreichbar',
+};
+
+const GENERIC_HTTP_TITLES = new Set([
+  'not found',
+  'unauthorized',
+  'forbidden',
+  'internal server error',
+  'bad request',
+  'service unavailable',
+]);
+
+/** Normalize any thrown value into a stable backend error object. */
+export function backendErrorFrom(err) {
+  if (!err) {
+    return { message: 'Unbekannter Fehler', status: null, path: null, method: null };
+  }
+  if (typeof err === 'string') {
+    return { message: err, status: null, path: null, method: null };
+  }
+  if (err.message != null && (err.status != null || err.path != null || err.method != null)) {
+    return {
+      message: err.message,
+      status: err.status ?? null,
+      path: err.path ?? null,
+      method: err.method ?? null,
+    };
+  }
+  if (err.message != null) {
+    return {
+      message: err.message,
+      status: err.status ?? null,
+      path: err.path ?? null,
+      method: err.method ?? null,
+    };
+  }
+  return { message: String(err), status: null, path: null, method: null };
+}
+
+/** Read structured error from a rejected RTK async thunk action. */
+export function resolveBackendError(action) {
+  if (action.payload) return backendErrorFrom(action.payload);
+  return backendErrorFrom(action.error);
+}
+
+export function formatBackendError(error) {
+  const normalized = backendErrorFrom(error);
+  const { message, status, path, method } = normalized;
+
+  const statusTitle = status != null ? STATUS_TITLES[status] : null;
+  const genericTitle =
+    message && GENERIC_HTTP_TITLES.has(message.trim().toLowerCase())
+      ? statusTitle
+      : null;
+
+  const title = statusTitle || genericTitle || (status != null ? `HTTP ${status}` : 'Backend-Fehler');
+
+  const detail =
+    message &&
+    message.trim().toLowerCase() !== title?.trim().toLowerCase() &&
+    !GENERIC_HTTP_TITLES.has(message.trim().toLowerCase())
+      ? message
+      : null;
+
+  const request = path ? `${method || 'GET'} ${path}` : null;
+
+  return { title, detail, status, request };
+}
+
+export function catchBackendError(rejectWithValue) {
+  return (err) => rejectWithValue(backendErrorFrom(err));
+}
+
+export function isBackendFailure(error) {
+  const normalized = backendErrorFrom(error);
+  return normalized.status != null || normalized.path != null;
+}
diff --git a/src/utils/companyForm.js b/src/utils/companyForm.js
index 2be730f..e6076af 100644
--- a/src/utils/companyForm.js
+++ b/src/utils/companyForm.js
@@ -16,3 +16,15 @@ export function companyLanguageToIso639(company) {
   if (company?.languageId === 2) return 'en';
   return 'de';
 }
+
+export function normalizeCompany(raw, overrides = {}) {
+  if (!raw) return null;
+  return {
+    id: raw.id,
+    name: overrides.name ?? raw.name ?? '',
+    iso639: overrides.iso639 ?? companyLanguageToIso639(raw),
+    taxrate: overrides.taxrate ?? raw.taxrate ?? null,
+    reducedtaxrate: overrides.reducedtaxrate ?? raw.reducedtaxrate ?? null,
+    rootCategoryId: overrides.rootCategoryId ?? raw.rootCategoryId ?? null,
+  };
+}
diff --git a/vite.config.js b/vite.config.js
index fb65761..2394f05 100644
--- a/vite.config.js
+++ b/vite.config.js
@@ -96,7 +96,7 @@ const sharedServer = {
   },
 };
 
-export default defineConfig({
+export default defineConfig(({ command }) => ({
   build: {
     rolldownOptions: {
       output: {
@@ -117,42 +117,48 @@ export default defineConfig({
   },
   plugins: [
     react(),
-    VitePWA({
-      registerType: 'autoUpdate',
-      manifest: {
-        id: '/',
-        name: 'Dashfront',
-        short_name: 'Dashfront',
-        start_url: '/',
-        scope: '/',
-        display: 'standalone',
-        background_color: '#dceeea',
-        theme_color: '#3b5bdb',
-        icons: [
-          {
-            src: '/icons/icon-192.png',
-            sizes: '192x192',
-            type: 'image/png',
-          },
-          {
-            src: '/icons/icon-512.png',
-            sizes: '512x512',
-            type: 'image/png',
-          },
-          {
-            src: '/icons/icon-512.png',
-            sizes: '512x512',
-            type: 'image/png',
-            purpose: 'maskable',
-          },
-        ],
-      },
-      workbox: {
-        globPatterns: ['**/*.{js,css,html,ico,png,svg,webmanifest,woff2}'],
-        navigateFallback: 'index.html',
-      },
-    }),
+    ...(command === 'build'
+      ? [
+          VitePWA({
+            registerType: 'autoUpdate',
+            injectRegister: 'auto',
+            manifest: {
+              id: '/',
+              name: 'Dashfront',
+              short_name: 'Dashfront',
+              start_url: '/',
+              scope: '/',
+              display: 'standalone',
+              background_color: '#dceeea',
+              theme_color: '#3b5bdb',
+              icons: [
+                {
+                  src: '/icons/icon-192.png',
+                  sizes: '192x192',
+                  type: 'image/png',
+                },
+                {
+                  src: '/icons/icon-512.png',
+                  sizes: '512x512',
+                  type: 'image/png',
+                },
+                {
+                  src: '/icons/icon-512.png',
+                  sizes: '512x512',
+                  type: 'image/png',
+                  purpose: 'maskable',
+                },
+              ],
+            },
+            workbox: {
+              globPatterns: ['**/*.{js,css,html,ico,png,svg,webmanifest,woff2}'],
+              navigateFallback: 'index.html',
+              navigateFallbackDenylist: [/^\/api/],
+            },
+          }),
+        ]
+      : []),
   ],
   server: sharedServer,
   preview: sharedServer,
-});
+}));