feat(imports): import history and delete by import

Track imports in DB, show history in Data section, allow deleting
transactions of a specific import instead of clearing all.

backend/src/routes/imports.ts

@@ -0,0 +1,36 @@
+import { Router } from 'express';
+import { pool } from '../db/pool';
+import { asyncHandler } from '../utils';
+import * as importsService from '../services/imports';
+
+const router = Router();
+
+router.get(
+  '/',
+  asyncHandler(async (_req, res) => {
+    const imports = await importsService.getImports();
+    res.json(imports);
+  }),
+);
+
+router.delete(
+  '/:id',
+  asyncHandler(async (req, res) => {
+    const id = Number(req.params.id);
+    if (isNaN(id)) {
+      res.status(400).json({ error: 'BAD_REQUEST', message: 'Invalid import id' });
+      return;
+    }
+
+    const { rows } = await pool.query('SELECT 1 FROM imports WHERE id = $1', [id]);
+    if (rows.length === 0) {
+      res.status(404).json({ error: 'NOT_FOUND', message: 'Import not found' });
+      return;
+    }
+
+    const result = await importsService.deleteImport(id);
+    res.json(result);
+  }),
+);
+
+export default router;