feat(ads): implement local interstitial ad display

- Replace TODO comment with actual implementation using LocalInterstitialAdDialog
- Add necessary import for LocalInterstitialAdDialog widget
- Update log message to reflect actual ad display

Author: fulleni

lib/ads/ad_navigator_observer.dart

@@ -4,6 +4,7 @@ import 'package:core/core.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_news_app_mobile_client_full_source_code/ads/ad_service.dart';
 import 'package:flutter_news_app_mobile_client_full_source_code/ads/models/ad_theme_style.dart';
+import 'package:flutter_news_app_mobile_client_full_source_code/ads/widgets/widgets.dart';
 import 'package:flutter_news_app_mobile_client_full_source_code/app/bloc/app_bloc.dart';
 import 'package:google_mobile_ads/google_mobile_ads.dart' as admob;
 import 'package:logging/logging.dart';
@@ -168,8 +169,13 @@ class AdNavigatorObserver extends NavigatorObserver {
         await admobInterstitialAd.show();
       } else if (interstitialAd.provider == AdPlatformType.local &&
           interstitialAd.adObject is LocalInterstitialAd) {
-        // TODO(fulleni): Implement showing local interstitial ad (e.g., via a dialog).
-        _logger.info('Showing local interstitial ad (placeholder).');
+        _logger.info('Showing local interstitial ad.');
+        await showDialog<void>(
+          context: navigator!.context,
+          builder: (context) => LocalInterstitialAdDialog(
+            localInterstitialAd: interstitialAd.adObject as LocalInterstitialAd,
+          ),
+        );
       }
     } else {
       _logger.info('No interstitial ad loaded.');