added product import and billing integration

lib/data/local/order_dao.dart

@@ -85,6 +85,46 @@ class OrderDao {
     });
   }
 
+  /// Reverses [commitSale]: deletes the order and its lines, adds the stock
+  /// back, and restores an attached customer's row exactly as passed in
+  /// (the caller supplies the pre-sale row — reconstructing it from deltas
+  /// here would get `last_visit_at` wrong).
+  Future<void> voidSale({
+    required String orderId,
+    required Map<String, double> stockMovements,
+    Map<String, Object?>? customerRow,
+  }) async {
+    await _db.transaction((txn) async {
+      await txn
+          .delete(Tables.orderItems, where: 'order_id = ?', whereArgs: [orderId]);
+      await txn.delete(Tables.orders, where: 'id = ?', whereArgs: [orderId]);
+
+      final batch = txn.batch();
+      final now = DateTime.now().millisecondsSinceEpoch;
+      stockMovements.forEach((id, qty) {
+        batch.rawUpdate(
+          'UPDATE ${Tables.products} SET stock = stock + ?, updated_at = ? '
+          'WHERE id = ?',
+          [qty, now, id],
+        );
+      });
+      if (customerRow != null) {
+        batch.update(
+          Tables.customers,
+          {
+            'loyalty_points': customerRow['loyalty_points'],
+            'lifetime_spend': customerRow['lifetime_spend'],
+            'visit_count': customerRow['visit_count'],
+            'last_visit_at': customerRow['last_visit_at'],
+          },
+          where: 'id = ?',
+          whereArgs: [customerRow['id']],
+        );
+      }
+      await batch.commit(noResult: true);
+    });
+  }
+
   Future<void> _insertOrder(DatabaseExecutor txn, SaleTransaction t) async {
     final cart = t.cart;