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,
+      },
+    );
+  }
+}

lib/features/booking/services/payment_service.dart

@@ -0,0 +1,67 @@
+// lib/features/booking/services/payment_service.dart
+
+import 'package:razorpay_flutter/razorpay_flutter.dart';
+import 'package:flutter/foundation.dart';
+
+typedef PaymentSuccessCallback = void Function(PaymentSuccessResponse response);
+typedef PaymentErrorCallback = void Function(PaymentFailureResponse response);
+typedef ExternalWalletCallback = void Function(ExternalWalletResponse response);
+
+class PaymentService {
+  late Razorpay _razorpay;
+
+  // Razorpay test key — matches web app
+  static const String _testKey = 'rzp_test_S49PVZmqAVoWSH';
+
+  PaymentSuccessCallback? onSuccess;
+  PaymentErrorCallback? onError;
+  ExternalWalletCallback? onExternalWallet;
+
+  void initialize({
+    required PaymentSuccessCallback onSuccess,
+    required PaymentErrorCallback onError,
+    ExternalWalletCallback? onExternalWallet,
+  }) {
+    _razorpay = Razorpay();
+    this.onSuccess = onSuccess;
+    this.onError = onError;
+    this.onExternalWallet = onExternalWallet;
+
+    _razorpay.on(Razorpay.EVENT_PAYMENT_SUCCESS, _handleSuccess);
+    _razorpay.on(Razorpay.EVENT_PAYMENT_ERROR, _handleError);
+    _razorpay.on(Razorpay.EVENT_EXTERNAL_WALLET, _handleExternalWallet);
+  }
+
+  void openPayment({
+    required double amount,
+    required String email,
+    required String phone,
+    required String eventName,
+    String? orderId,
+  }) {
+    final options = <String, dynamic>{
+      'key': _testKey,
+      'amount': (amount * 100).toInt(), // paise
+      'currency': 'INR',
+      'name': 'Eventify',
+      'description': 'Ticket: $eventName',
+      'prefill': {
+        'email': email,
+        'contact': phone,
+      },
+      'theme': {'color': '#0B63D6'},
+    };
+    if (orderId != null) options['order_id'] = orderId;
+
+    if (kDebugMode) debugPrint('PaymentService: opening Razorpay with amount=${amount * 100} paise');
+    _razorpay.open(options);
+  }
+
+  void _handleSuccess(PaymentSuccessResponse res) => onSuccess?.call(res);
+  void _handleError(PaymentFailureResponse res) => onError?.call(res);
+  void _handleExternalWallet(ExternalWalletResponse res) => onExternalWallet?.call(res);
+
+  void dispose() {
+    _razorpay.clear();
+  }
+}