feat: Phase 1 critical gaps — gamification API, Razorpay checkout, Google OAuth, notifications

- Fix gamification endpoints to use Node.js server (app.eventifyplus.com)
- Replace 6 mock gamification methods with real API calls (dashboard, leaderboard, shop, redeem, submit)
- Add booking models, service, payment service (Razorpay), checkout provider
- Add 3-step CheckoutScreen with Razorpay native modal integration
- Add Google OAuth login (Flutter + Django backend)
- Add full notifications system (Django model + 3 endpoints + Flutter UI)
- Register CheckoutProvider, NotificationProvider in main.dart MultiProvider
- Wire notification bell in HomeScreen app bar
- Add razorpay_flutter ^1.3.7 and google_sign_in ^6.2.2 packages

lib/features/notifications/providers/notification_provider.dart

@@ -0,0 +1,72 @@
+// lib/features/notifications/providers/notification_provider.dart
+
+import 'package:flutter/foundation.dart';
+import '../../../core/utils/error_utils.dart';
+import '../models/notification_model.dart';
+import '../services/notification_service.dart';
+
+class NotificationProvider extends ChangeNotifier {
+  final NotificationService _service = NotificationService();
+
+  List<NotificationModel> notifications = [];
+  int unreadCount = 0;
+  bool loading = false;
+  String? error;
+
+  /// Load full notification list.
+  Future<void> loadNotifications() async {
+    loading = true;
+    error = null;
+    notifyListeners();
+    try {
+      notifications = await _service.getNotifications();
+      unreadCount = notifications.where((n) => !n.isRead).length;
+    } catch (e) {
+      error = userFriendlyError(e);
+    } finally {
+      loading = false;
+      notifyListeners();
+    }
+  }
+
+  /// Lightweight count refresh (no full list fetch).
+  Future<void> refreshUnreadCount() async {
+    try {
+      unreadCount = await _service.getUnreadCount();
+      notifyListeners();
+    } catch (_) {
+      // Silently fail — badge just won't update
+    }
+  }
+
+  /// Mark single notification as read.
+  Future<void> markAsRead(int id) async {
+    try {
+      await _service.markAsRead(notificationId: id);
+      final idx = notifications.indexWhere((n) => n.id == id);
+      if (idx >= 0) {
+        notifications[idx].isRead = true;
+        unreadCount = notifications.where((n) => !n.isRead).length;
+        notifyListeners();
+      }
+    } catch (e) {
+      error = userFriendlyError(e);
+      notifyListeners();
+    }
+  }
+
+  /// Mark all as read.
+  Future<void> markAllAsRead() async {
+    try {
+      await _service.markAsRead(); // null = mark all
+      for (final n in notifications) {
+        n.isRead = true;
+      }
+      unreadCount = 0;
+      notifyListeners();
+    } catch (e) {
+      error = userFriendlyError(e);
+      notifyListeners();
+    }
+  }
+}