feat: add message translation support

- Introduced translation functionality in chat screen, allowing users to translate messages before sending.
- Added MessageTranslationButton to the input bar for enabling/disabling translation.
- Implemented translation service to handle incoming and outgoing text translations using llama models.
- Enhanced message storage to include original and translated text, language codes, and translation status.
- Created UI components for displaying translated messages and managing translation options.
- Added translation model management, including downloading and storing models locally.
- Updated app settings to manage translation preferences and model selections.

lib/services/app_settings_service.dart

@@ -1,6 +1,7 @@
 import 'dart:convert';
 import 'package:flutter/foundation.dart';
 import '../models/app_settings.dart';
+import '../models/translation_support.dart';
 import '../storage/prefs_manager.dart';
 import '../utils/app_logger.dart';
 
@@ -222,4 +223,34 @@ class AppSettingsService extends ChangeNotifier {
   Future<void> setJumpToOldestUnread(bool value) async {
     await updateSettings(_settings.copyWith(jumpToOldestUnread: value));
   }
+
+  Future<void> setTranslationEnabled(bool value) async {
+    await updateSettings(_settings.copyWith(translationEnabled: value));
+  }
+
+  Future<void> setTranslationTargetLanguageCode(String? value) async {
+    await updateSettings(
+      _settings.copyWith(translationTargetLanguageCode: value),
+    );
+  }
+
+  Future<void> setComposerTranslationEnabled(bool value) async {
+    await updateSettings(_settings.copyWith(composerTranslationEnabled: value));
+  }
+
+  Future<void> setTranslationModelSourceUrl(String? value) async {
+    await updateSettings(_settings.copyWith(translationModelSourceUrl: value));
+  }
+
+  Future<void> setTranslationSelectedModelId(String? value) async {
+    await updateSettings(_settings.copyWith(translationSelectedModelId: value));
+  }
+
+  Future<void> setTranslationDownloadedModels(
+    List<TranslationModelRecord> value,
+  ) async {
+    await updateSettings(
+      _settings.copyWith(translationDownloadedModels: value),
+    );
+  }
 }