Implement navigation and view management in DataViewer, adding Dashboard and TableManagement components. Update export data handling based on current view. Create new components for managing Kreditor, Konto, and BU tables with CRUD functionality. Refactor admin routes to remove admin access checks and streamline data handling for various entities.

client/src/components/TableManagement.js

@@ -0,0 +1,76 @@
+import React, { Component } from 'react';
+import {
+  Box,
+  Tabs,
+  Tab,
+  Paper,
+  Typography,
+} from '@mui/material';
+import {
+  AccountBalance as KreditorIcon,
+  AccountBalanceWallet as KontoIcon,
+  Receipt as BUIcon,
+} from '@mui/icons-material';
+import KreditorTable from './admin/KreditorTable';
+import KontoTable from './admin/KontoTable';
+import BUTable from './admin/BUTable';
+
+class TableManagement extends Component {
+  constructor(props) {
+    super(props);
+    this.state = {
+      activeTab: 0,
+    };
+  }
+
+  handleTabChange = (event, newValue) => {
+    this.setState({ activeTab: newValue });
+  };
+
+  render() {
+    const { activeTab } = this.state;
+    const { user } = this.props;
+
+    return (
+      <Box>
+        <Typography variant="h4" component="h1" gutterBottom>
+          Stammdaten verwalten
+        </Typography>
+        
+        <Paper elevation={2}>
+          <Box sx={{ borderBottom: 1, borderColor: 'divider' }}>
+            <Tabs 
+              value={activeTab} 
+              onChange={this.handleTabChange}
+              variant="fullWidth"
+            >
+              <Tab 
+                icon={<KreditorIcon />} 
+                label="Kreditoren" 
+                sx={{ minHeight: 64 }}
+              />
+              <Tab 
+                icon={<KontoIcon />} 
+                label="Konten" 
+                sx={{ minHeight: 64 }}
+              />
+              <Tab 
+                icon={<BUIcon />} 
+                label="Buchungsschlüssel" 
+                sx={{ minHeight: 64 }}
+              />
+            </Tabs>
+          </Box>
+
+          <Box sx={{ p: 3 }}>
+            {activeTab === 0 && <KreditorTable user={user} />}
+            {activeTab === 1 && <KontoTable user={user} />}
+            {activeTab === 2 && <BUTable user={user} />}
+          </Box>
+        </Paper>
+      </Box>
+    );
+  }
+}
+
+export default TableManagement;