feat: make server owner of tabs

lib/viewmodels/bar_screen_view_model.dart

@@ -10,7 +10,6 @@ import '../models/payment_method.dart';
 import '../models/product.dart';
 import '../models/tab_item.dart';
 import '../services/bar_tab_service.dart';
-import '../services/product_service.dart';
 
 /// Tabs come from a database stream, so every change (local or remote) shows
 /// up without manual reloads. Actions report to Sentry and rethrow; the view
@@ -129,12 +128,9 @@ class BarScreenViewModel extends ChangeNotifier {
     );
   }
 
-  /// Running out of stock is an expected outcome, not a bug worth reporting.
   Future<T> _guard<T>(String action, Future<T> Function() body) async {
     try {
       return await body();
-    } on InsufficientStockException {
-      rethrow;
     } catch (e, stack) {
       debugPrint('BarScreenViewModel: $action error: $e');
       unawaited(Sentry.captureException(e, stackTrace: stack));