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/screens/booking_screen.dart

@@ -1,15 +1,19 @@
 // lib/screens/booking_screen.dart
 import 'package:flutter/material.dart';
+import 'checkout_screen.dart';
 
 class BookingScreen extends StatefulWidget {
-  // Keep onBook in the constructor if you want to use it later, but we won't call it here.
   final VoidCallback? onBook;
   final String image;
+  final int? eventId;
+  final String? eventName;
 
   const BookingScreen({
     Key? key,
     this.onBook,
     this.image = 'assets/images/event1.jpg',
+    this.eventId,
+    this.eventName,
   }) : super(key: key);
 
   @override
@@ -39,11 +43,22 @@ Whether you're a longtime fan or hearing him live for the first time, this eveni
   bool _booked = false;
 
   void _performLocalBooking() {
-    // mark locally booked (do NOT call widget.onBook())
+    // If event data is available, navigate to real checkout
+    if (widget.eventId != null) {
+      Navigator.of(context).push(MaterialPageRoute(
+        builder: (_) => CheckoutScreen(
+          eventId: widget.eventId!,
+          eventName: widget.eventName ?? 'Event',
+          eventImage: widget.image,
+        ),
+      ));
+      return;
+    }
+    // Fallback: demo booking for events without IDs
     if (!_booked) {
       setState(() => _booked = true);
       ScaffoldMessenger.of(context).showSnackBar(
-        SnackBar(content: Text('Tickets booked (demo)')),
+        const SnackBar(content: Text('Tickets booked (demo)')),
       );
     }
   }