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

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/features/booking/services/booking_service.dart

@@ -0,0 +1,53 @@
+// lib/features/booking/services/booking_service.dart
+
+import '../../../core/api/api_client.dart';
+import '../../../core/api/api_endpoints.dart';
+import '../models/booking_models.dart';
+
+class BookingService {
+  final ApiClient _api = ApiClient();
+
+  /// Fetch available ticket types for an event.
+  Future<List<TicketMetaModel>> getTicketMeta(int eventId) async {
+    final res = await _api.post(
+      ApiEndpoints.ticketMetaList,
+      body: {'event_id': eventId},
+    );
+    final rawList = res['ticket_metas'] ?? res['tickets'] ?? res['data'] ?? [];
+    if (rawList is List) {
+      return rawList
+          .map((e) => TicketMetaModel.fromJson(Map<String, dynamic>.from(e as Map)))
+          .toList();
+    }
+    return [];
+  }
+
+  /// Add item to cart.
+  Future<Map<String, dynamic>> addToCart({
+    required int ticketMetaId,
+    required int quantity,
+  }) async {
+    return await _api.post(
+      ApiEndpoints.cartAdd,
+      body: {'ticket_meta_id': ticketMetaId, 'quantity': quantity},
+    );
+  }
+
+  /// Process checkout — creates booking + returns order ID for payment.
+  Future<Map<String, dynamic>> processCheckout({
+    required int eventId,
+    required List<Map<String, dynamic>> tickets,
+    required Map<String, dynamic> shippingDetails,
+    String? couponCode,
+  }) async {
+    return await _api.post(
+      ApiEndpoints.checkout,
+      body: {
+        'event_id': eventId,
+        'tickets': tickets,
+        'shipping': shippingDetails,
+        if (couponCode != null) 'coupon_code': couponCode,
+      },
+    );
+  }
+}