feat: Add Text-to-Speech settings and customization options

- Introduced new preference keys for TTS settings: voice, speech rate, pitch, and volume.
- Updated SettingsService to handle TTS settings and persist them.
- Enhanced AppSettings to include TTS-related properties.
- Implemented TTS settings UI in AppCustomizationPage, allowing users to select voice and adjust speech parameters.
- Added localization support for TTS settings in multiple languages.

lib/l10n/app_localizations_en.dart

@@ -887,6 +887,47 @@ class AppLocalizationsEn extends AppLocalizations {
   String get sendOnEnterDescription =>
       'Enter sends (soft keyboard). Cmd/Ctrl+Enter also available';
 
+  @override
+  String get ttsSettings => 'Text to Speech';
+
+  @override
+  String get ttsVoice => 'Voice';
+
+  @override
+  String get ttsSpeechRate => 'Speech Rate';
+
+  @override
+  String get ttsPitch => 'Pitch';
+
+  @override
+  String get ttsVolume => 'Volume';
+
+  @override
+  String get ttsPreview => 'Preview Voice';
+
+  @override
+  String get ttsSystemDefault => 'System Default';
+
+  @override
+  String get ttsSelectVoice => 'Select Voice';
+
+  @override
+  String get ttsPreviewText => 'This is a preview of the selected voice.';
+
+  @override
+  String get ttsNoVoicesAvailable => 'No voices available';
+
+  @override
+  String ttsVoicesForLanguage(String language) {
+    return '$language Voices';
+  }
+
+  @override
+  String get ttsOtherVoices => 'Other Languages';
+
+  @override
+  String get error => 'Error';
+
   @override
   String get display => 'Display';