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/notifications/widgets/notification_panel.dart

@@ -0,0 +1,101 @@
+// lib/features/notifications/widgets/notification_panel.dart
+
+import 'package:flutter/material.dart';
+import 'package:provider/provider.dart';
+import '../providers/notification_provider.dart';
+import 'notification_tile.dart';
+
+class NotificationPanel extends StatelessWidget {
+  const NotificationPanel({Key? key}) : super(key: key);
+
+  @override
+  Widget build(BuildContext context) {
+    return DraggableScrollableSheet(
+      expand: false,
+      initialChildSize: 0.6,
+      minChildSize: 0.35,
+      maxChildSize: 0.95,
+      builder: (context, scrollController) {
+        return Container(
+          decoration: const BoxDecoration(
+            color: Colors.white,
+            borderRadius: BorderRadius.vertical(top: Radius.circular(24)),
+          ),
+          child: Column(
+            children: [
+              // Handle bar
+              Center(
+                child: Container(
+                  margin: const EdgeInsets.only(top: 12, bottom: 8),
+                  width: 48,
+                  height: 5,
+                  decoration: BoxDecoration(
+                    color: Colors.grey.shade300,
+                    borderRadius: BorderRadius.circular(3),
+                  ),
+                ),
+              ),
+              // Header
+              Padding(
+                padding: const EdgeInsets.symmetric(horizontal: 20, vertical: 8),
+                child: Row(
+                  mainAxisAlignment: MainAxisAlignment.spaceBetween,
+                  children: [
+                    const Text('Notifications', style: TextStyle(fontSize: 20, fontWeight: FontWeight.w700)),
+                    Consumer<NotificationProvider>(
+                      builder: (_, provider, __) {
+                        if (provider.unreadCount == 0) return const SizedBox.shrink();
+                        return TextButton(
+                          onPressed: provider.markAllAsRead,
+                          child: const Text('Mark all read', style: TextStyle(fontSize: 13)),
+                        );
+                      },
+                    ),
+                  ],
+                ),
+              ),
+              const Divider(height: 1),
+              // List
+              Expanded(
+                child: Consumer<NotificationProvider>(
+                  builder: (_, provider, __) {
+                    if (provider.loading) {
+                      return const Center(child: CircularProgressIndicator());
+                    }
+                    if (provider.notifications.isEmpty) {
+                      return Center(
+                        child: Column(
+                          mainAxisSize: MainAxisSize.min,
+                          children: [
+                            Icon(Icons.notifications_none, size: 56, color: Colors.grey.shade300),
+                            const SizedBox(height: 12),
+                            Text('No notifications yet', style: TextStyle(color: Colors.grey.shade500, fontSize: 15)),
+                          ],
+                        ),
+                      );
+                    }
+                    return ListView.separated(
+                      controller: scrollController,
+                      padding: const EdgeInsets.symmetric(vertical: 8),
+                      itemCount: provider.notifications.length,
+                      separatorBuilder: (_, __) => const Divider(height: 1, indent: 72),
+                      itemBuilder: (ctx, idx) {
+                        final notif = provider.notifications[idx];
+                        return NotificationTile(
+                          notification: notif,
+                          onTap: () {
+                            if (!notif.isRead) provider.markAsRead(notif.id);
+                          },
+                        );
+                      },
+                    );
+                  },
+                ),
+              ),
+            ],
+          ),
+        );
+      },
+    );
+  }
+}