feat: Add demo verification code message

- Added localization keys
- Added english translation
- Added arabic translation

Author: fulleni

lib/l10n/app_localizations.dart

@@ -1381,6 +1381,12 @@ abstract class AppLocalizations {
   /// In en, this message translates to:
   /// **'Start following categories to see them here.'**
   String get followedCategoriesEmptySubheadline;
+
+  /// Message shown in demo mode to provide the verification code
+  ///
+  /// In en, this message translates to:
+  /// **'Demo Mode: Use code {code}'**
+  String demoVerificationCodeMessage(String code);
 }
 
 class _AppLocalizationsDelegate

lib/l10n/app_localizations_ar.dart

@@ -705,4 +705,9 @@ class AppLocalizationsAr extends AppLocalizations {
   @override
   String get followedCategoriesEmptySubheadline =>
       'Start following categories to see them here.';
+
+  @override
+  String demoVerificationCodeMessage(String code) {
+    return 'وضع العرض التوضيحي: استخدم الرمز $code';
+  }
 }

lib/l10n/app_localizations_en.dart

@@ -707,4 +707,9 @@ class AppLocalizationsEn extends AppLocalizations {
   @override
   String get followedCategoriesEmptySubheadline =>
       'Start following categories to see them here.';
+
+  @override
+  String demoVerificationCodeMessage(String code) {
+    return 'Demo Mode: Use code $code';
+  }
 }