refactor: Update message hint text for improved user guidance

- Changed the placeholder text in the message input field across multiple languages to "Ask Conduit" for better clarity and user engagement.
- Updated localization files for German, English, Spanish, French, Italian, Dutch, Russian, and Chinese to reflect the new hint text.

lib/l10n/app_localizations_fr.dart

@@ -456,7 +456,7 @@ class AppLocalizationsFr extends AppLocalizations {
   String get messageInputHint => 'Saisissez votre message';
 
   @override
-  String get messageHintText => 'Message...';
+  String get messageHintText => 'Demander à Conduit';
 
   @override
   String get stopGenerating => 'Arrêter la génération';