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/widgets/notification_bell.dart

@@ -0,0 +1,61 @@
+// lib/features/notifications/widgets/notification_bell.dart
+
+import 'package:flutter/material.dart';
+import 'package:provider/provider.dart';
+import '../providers/notification_provider.dart';
+import 'notification_panel.dart';
+
+class NotificationBell extends StatelessWidget {
+  const NotificationBell({Key? key}) : super(key: key);
+
+  @override
+  Widget build(BuildContext context) {
+    return Consumer<NotificationProvider>(
+      builder: (context, provider, _) {
+        return GestureDetector(
+          onTap: () => _showPanel(context),
+          child: Stack(
+            clipBehavior: Clip.none,
+            children: [
+              const Padding(
+                padding: EdgeInsets.all(8.0),
+                child: Icon(Icons.notifications_outlined, size: 26, color: Colors.black87),
+              ),
+              if (provider.unreadCount > 0)
+                Positioned(
+                  right: 4,
+                  top: 4,
+                  child: Container(
+                    padding: const EdgeInsets.symmetric(horizontal: 5, vertical: 2),
+                    decoration: BoxDecoration(
+                      color: Colors.red,
+                      borderRadius: BorderRadius.circular(10),
+                    ),
+                    constraints: const BoxConstraints(minWidth: 18, minHeight: 18),
+                    child: Text(
+                      provider.unreadCount > 99 ? '99+' : '${provider.unreadCount}',
+                      style: const TextStyle(color: Colors.white, fontSize: 10, fontWeight: FontWeight.w600),
+                      textAlign: TextAlign.center,
+                    ),
+                  ),
+                ),
+            ],
+          ),
+        );
+      },
+    );
+  }
+
+  void _showPanel(BuildContext context) {
+    context.read<NotificationProvider>().loadNotifications();
+    showModalBottomSheet(
+      context: context,
+      isScrollControlled: true,
+      backgroundColor: Colors.transparent,
+      builder: (_) => ChangeNotifierProvider.value(
+        value: context.read<NotificationProvider>(),
+        child: const NotificationPanel(),
+      ),
+    );
+  }
+}