Enhance Accounting Items Management with JTL Kontierung Integration

- Added a new API route to fetch JTL Kontierung data based on transaction ID.
- Implemented loading of JTL Kontierung data in the AccountingItemsManager component.
- Updated UI to display JTL Kontierung data for debugging purposes.
- Enhanced user feedback during processing tasks in the App component with tooltips and progress indicators.

client/src/components/AccountingItemsManager.js

@@ -44,6 +44,7 @@ class AccountingItemsManager extends Component {
       editingItem: null,
       showCreateDialog: false,
       showCreateKontoDialog: false,
+      jtlKontierung: null,
       newItem: {
         umsatz_brutto: '',
         soll_haben_kz: 'S',
@@ -65,6 +66,7 @@ class AccountingItemsManager extends Component {
 
   componentDidMount() {
     this.loadData();
+    this.loadJtlKontierung();
   }
 
   loadData = async () => {
@@ -88,6 +90,31 @@ class AccountingItemsManager extends Component {
     }
   };
 
+  loadJtlKontierung = async () => {
+    try {
+      const { transaction } = this.props;
+      if (!transaction || !transaction.jtlId) {
+        this.setState({ jtlKontierung: undefined });
+        return;
+      }
+
+      const response = await this.authService.apiCall(`/data/jtl-kontierung/${transaction.jtlId}`);
+      if (!response) return;
+
+      if (response.ok) {
+        const data = await response.json();
+        this.setState({ jtlKontierung: data });
+      } else {
+        const err = await response.json();
+        console.error('Failed to load JTL Kontierung:', err);
+        this.setState({ jtlKontierung: undefined });
+      }
+    } catch (e) {
+      console.error('Error loading JTL Kontierung:', e);
+      this.setState({ jtlKontierung: undefined });
+    }
+  }
+
   loadAccountingItems = async () => {
     const { transaction } = this.props;
     if (!transaction?.id) return;
@@ -319,6 +346,21 @@ class AccountingItemsManager extends Component {
           />
         </Box>
 
+        {transaction?.jtlId && (
+          <Box sx={{ mb: 2, p: 2, border: '1px dashed #999', borderRadius: 1 }}>
+            <Typography variant="subtitle2">Debug: tUmsatzKontierung.data</Typography>
+            <Typography variant="caption" component="div" sx={{ whiteSpace: 'pre-wrap', wordBreak: 'break-word' }}>
+              {this.state.jtlKontierung === undefined
+                ? 'undefined'
+                : this.state.jtlKontierung === null
+                  ? 'null'
+                  : typeof this.state.jtlKontierung === 'object'
+                    ? JSON.stringify(this.state.jtlKontierung, null, 2)
+                    : String(this.state.jtlKontierung)}
+            </Typography>
+          </Box>
+        )}
+
         <TableContainer component={Paper}>
           <Table size="small">
             <TableHead>