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/services/imports.ts

@@ -0,0 +1,44 @@
+import { pool } from '../db/pool';
+import type { Import } from '@family-budget/shared';
+
+export async function getImports(): Promise<Import[]> {
+  const result = await pool.query(
+    `SELECT
+       i.id,
+       i.imported_at,
+       i.account_id,
+       a.alias AS account_alias,
+       i.bank,
+       i.account_number_masked,
+       i.imported_count,
+       i.duplicates_skipped,
+       i.total_in_file
+     FROM imports i
+     LEFT JOIN accounts a ON a.id = i.account_id
+     ORDER BY i.imported_at DESC`,
+  );
+
+  return result.rows.map((r) => ({
+    id: Number(r.id),
+    importedAt: r.imported_at.toISOString(),
+    accountId: r.account_id != null ? Number(r.account_id) : null,
+    accountAlias: r.account_alias ?? null,
+    bank: r.bank,
+    accountNumberMasked: r.account_number_masked,
+    importedCount: Number(r.imported_count),
+    duplicatesSkipped: Number(r.duplicates_skipped),
+    totalInFile: Number(r.total_in_file),
+  }));
+}
+
+export async function deleteImport(id: number): Promise<{ deleted: number }> {
+  const result = await pool.query(
+    'DELETE FROM transactions WHERE import_id = $1 RETURNING id',
+    [id],
+  );
+  const deleted = result.rowCount ?? 0;
+
+  await pool.query('DELETE FROM imports WHERE id = $1', [id]);
+
+  return { deleted };
+}