fix(ads): prevent interstitial ads from being dismissed by tapping outside

- Add 'await' keyword to showDialog calls for better async handling
- Set 'barrierDismissible' to false in both _showLocalAd and _showDemoAd
- Improve code comments for clarity

Author: fulleni

lib/ads/interstitial_ad_manager.dart

@@ -267,17 +267,21 @@ class InterstitialAdManager {
 
   Future<void> _showLocalAd(BuildContext context, InterstitialAd ad) async {
     if (ad.adObject is! LocalInterstitialAd) return;
+    // Await the result of showDialog, which completes when the dialog is popped.
     await showDialog<void>(
       context: context,
+      barrierDismissible: false, // Prevent dismissing by tapping outside
       builder: (_) => LocalInterstitialAdDialog(
         localInterstitialAd: ad.adObject as LocalInterstitialAd,
       ),
     );
   }
 
   Future<void> _showDemoAd(BuildContext context) async {
+    // Await the result of showDialog, which completes when the dialog is popped.
     await showDialog<void>(
       context: context,
+      barrierDismissible: false, // Prevent dismissing by tapping outside
       builder: (_) => const DemoInterstitialAdDialog(),
     );
   }