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.

src/routes/data/accountingItems.js

@@ -3,6 +3,39 @@ const { authenticateToken } = require('../../middleware/auth');
 
 const router = express.Router();
 
+// Debug: Get JTL Kontierung data for a specific JTL Umsatz (by kZahlungsabgleichUmsatz)
+router.get('/jtl-kontierung/:jtlId', authenticateToken, async (req, res) => {
+  try {
+    const { executeQuery } = require('../../config/database');
+    const { jtlId } = req.params;
+
+    const query = `
+      SELECT
+        uk.data
+      FROM eazybusiness.dbo.tZahlungsabgleichUmsatz z
+      LEFT JOIN eazybusiness.dbo.tUmsatzKontierung uk
+        ON uk.kZahlungsabgleichUmsatz = z.kZahlungsabgleichUmsatz
+      WHERE z.kZahlungsabgleichUmsatz = @jtlId
+    `;
+
+    const result = await executeQuery(query, { jtlId: parseInt(jtlId, 10) });
+    // Return undefined when no data found (do not lie with empty array/string)
+    if (!result.recordset || result.recordset.length === 0) {
+      return res.json({ data: undefined });
+    }
+
+    // If multiple rows exist, return all; otherwise single object
+    const rows = result.recordset.map(r => ({ data: r.data }));
+    if (rows.length === 1) {
+      return res.json(rows[0]);
+    }
+    return res.json(rows);
+  } catch (error) {
+    console.error('Error fetching JTL Kontierung data:', error);
+    res.status(500).json({ error: 'Failed to fetch JTL Kontierung data' });
+  }
+});
+
 // Get accounting items for a specific transaction
 router.get('/accounting-items/:transactionId', authenticateToken, async (req, res) => {
   try {