feat(ads): integrate InterstitialAdManager and navigatorKey in bootstrap

- Add import for InterstitialAdManager
- Create GlobalKey<NavigatorState> for BuildContext access
- Pass navigatorKey to App for use by AppBloc and InterstitialAdManager

Author: fulleni

lib/bootstrap.dart

@@ -18,6 +18,7 @@ import 'package:flutter_news_app_mobile_client_full_source_code/ads/ad_service.d
 import 'package:flutter_news_app_mobile_client_full_source_code/ads/admob_ad_provider.dart'
     if (dart.library.io) 'package:flutter_news_app_mobile_client_full_source_code/ads/admob_ad_provider.dart';
 import 'package:flutter_news_app_mobile_client_full_source_code/ads/demo_ad_provider.dart';
+import 'package:flutter_news_app_mobile_client_full_source_code/ads/interstitial_ad_manager.dart';
 import 'package:flutter_news_app_mobile_client_full_source_code/ads/local_ad_provider.dart';
 import 'package:flutter_news_app_mobile_client_full_source_code/app/app.dart';
 import 'package:flutter_news_app_mobile_client_full_source_code/app/config/config.dart'
@@ -137,6 +138,10 @@ Future<Widget> bootstrap(
   // This ensures the AppBloc starts with an accurate authentication status.
   final initialUser = await authenticationRepository.getCurrentUser();
 
+  // Create a GlobalKey for the NavigatorState to be used by AppBloc
+  // and InterstitialAdManager for BuildContext access.
+  final GlobalKey<NavigatorState> navigatorKey = GlobalKey<NavigatorState>();
+
   // 4. Initialize all other DataClients and Repositories.
   // These now also have a guaranteed valid httpClient.
   DataClient<Headline> headlinesClient;
@@ -417,5 +422,6 @@ Future<Widget> bootstrap(
     adService: adService,
     initialUser: initialUser,
     localAdRepository: localAdRepository,
+    navigatorKey: navigatorKey, // Pass the navigatorKey to App
   );
 }