feat: Implement Firebase push notifications with support for flavor-specific configurations.

lib/core/widgets/app_shell.dart

@@ -1,14 +1,34 @@
 import 'package:flutter/material.dart';
+import 'package:go_router/go_router.dart';
+import 'package:real_estate_mobile/core/services/push_notification_service.dart';
 import 'package:real_estate_mobile/core/widgets/app_bottom_nav_bar.dart';
 import 'package:real_estate_mobile/features/home/presentation/widgets/home_header.dart';
 
 /// Root shell that provides the persistent header and bottom nav bar.
 /// Only the content area (child) swaps when navigating between tabs.
-class AppShell extends StatelessWidget {
+class AppShell extends StatefulWidget {
   final Widget child;
 
   const AppShell({super.key, required this.child});
 
+  @override
+  State<AppShell> createState() => _AppShellState();
+}
+
+class _AppShellState extends State<AppShell> {
+  @override
+  void initState() {
+    super.initState();
+    // Wire push notification taps to GoRouter navigation
+    PushNotificationService().onNotificationTap = (actionUrl) {
+      if (mounted && actionUrl != null && actionUrl.isNotEmpty) {
+        context.go(actionUrl);
+      } else if (mounted) {
+        context.go('/notifications');
+      }
+    };
+  }
+
   @override
   Widget build(BuildContext context) {
     return Scaffold(
@@ -31,8 +51,8 @@ class AppShell extends StatelessWidget {
                 );
               },
               child: KeyedSubtree(
-                key: ValueKey(child.runtimeType),
-                child: child,
+                key: ValueKey(widget.child.runtimeType),
+                child: widget.child,
               ),
             ),
           ),