refactor(ads): update demo ad widgets to use localization

- Replace hardcoded strings with localized versions in banner, interstitial, and native ad widgets
- Add import for AppLocalizations in all affected files
- Update text content to use localized strings from AppLocalizations

Author: fulleni

lib/ads/widgets/demo_banner_ad_widget.dart

@@ -1,5 +1,6 @@
 import 'package:core/core.dart';
 import 'package:flutter/material.dart';
+import 'package:flutter_news_app_mobile_client_full_source_code/l10n/app_localizations.dart';
 import 'package:ui_kit/ui_kit.dart';
 
 /// {@template demo_banner_ad_widget}
@@ -37,7 +38,7 @@ class DemoBannerAdWidget extends StatelessWidget {
         width: double.infinity,
         child: Center(
           child: Text(
-            'BANNER AD (DEMO)',
+            AppLocalizations.of(context).demoBannerAdText,
             style: theme.textTheme.titleMedium?.copyWith(
               color: theme.colorScheme.onSurfaceVariant,
             ),

lib/ads/widgets/demo_interstitial_ad_dialog.dart

@@ -1,5 +1,6 @@
 import 'package:flutter/material.dart';
 import 'package:go_router/go_router.dart';
+import 'package:flutter_news_app_mobile_client_full_source_code/l10n/app_localizations.dart';
 import 'package:ui_kit/ui_kit.dart';
 
 /// {@template demo_interstitial_ad_dialog}
@@ -25,15 +26,15 @@ class DemoInterstitialAdDialog extends StatelessWidget {
                 mainAxisAlignment: MainAxisAlignment.center,
                 children: [
                   Text(
-                    'INTERSTITIAL AD (DEMO)',
+                    AppLocalizations.of(context).demoInterstitialAdText,
                     style: theme.textTheme.titleLarge?.copyWith(
                       color: theme.colorScheme.onSurface,
                     ),
                     textAlign: TextAlign.center,
                   ),
                   const SizedBox(height: AppSpacing.md),
                   Text(
-                    'This is a full-screen advertisement placeholder.',
+                    AppLocalizations.of(context).demoInterstitialAdDescription,
                     style: theme.textTheme.bodyMedium?.copyWith(
                       color: theme.colorScheme.onSurfaceVariant,
                     ),

lib/ads/widgets/demo_native_ad_widget.dart

@@ -1,5 +1,6 @@
 import 'package:core/core.dart';
 import 'package:flutter/material.dart';
+import 'package:flutter_news_app_mobile_client_full_source_code/l10n/app_localizations.dart';
 import 'package:ui_kit/ui_kit.dart';
 
 /// {@template demo_native_ad_widget}
@@ -10,17 +11,15 @@ import 'package:ui_kit/ui_kit.dart';
 /// {@endtemplate}
 class DemoNativeAdWidget extends StatelessWidget {
   /// {@macro demo_native_ad_widget}
-  const DemoNativeAdWidget({
-    this.headlineImageStyle,
-    super.key,
-  });
+  const DemoNativeAdWidget({this.headlineImageStyle, super.key});
 
   /// The user's preference for feed layout, used to determine the ad's visual size.
   final HeadlineImageStyle? headlineImageStyle;
 
   @override
   Widget build(BuildContext context) {
     final theme = Theme.of(context);
+    final l10n = AppLocalizations.of(context);
 
     // Determine the height based on the headlineImageStyle, mimicking real ad widgets.
     final double adHeight = headlineImageStyle == HeadlineImageStyle.largeThumbnail
@@ -37,7 +36,7 @@ class DemoNativeAdWidget extends StatelessWidget {
         width: double.infinity,
         child: Center(
           child: Text(
-            'NATIVE AD (DEMO)',
+            l10n.demoNativeAdText,
             style: theme.textTheme.titleMedium?.copyWith(
               color: theme.colorScheme.onSurfaceVariant,
             ),
@@ -48,3 +47,4 @@ class DemoNativeAdWidget extends StatelessWidget {
     );
   }
 }
+