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

macos/Flutter/GeneratedPluginRegistrant.swift

@@ -7,6 +7,7 @@ import Foundation
 
 import file_selector_macos
 import geolocator_apple
+import google_sign_in_ios
 import path_provider_foundation
 import share_plus
 import shared_preferences_foundation
@@ -17,6 +18,7 @@ import video_player_avfoundation
 func RegisterGeneratedPlugins(registry: FlutterPluginRegistry) {
   FileSelectorPlugin.register(with: registry.registrar(forPlugin: "FileSelectorPlugin"))
   GeolocatorPlugin.register(with: registry.registrar(forPlugin: "GeolocatorPlugin"))
+  FLTGoogleSignInPlugin.register(with: registry.registrar(forPlugin: "FLTGoogleSignInPlugin"))
   PathProviderPlugin.register(with: registry.registrar(forPlugin: "PathProviderPlugin"))
   SharePlusMacosPlugin.register(with: registry.registrar(forPlugin: "SharePlusMacosPlugin"))
   SharedPreferencesPlugin.register(with: registry.registrar(forPlugin: "SharedPreferencesPlugin"))