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_es.arb

@@ -309,6 +309,19 @@
   "chatSettings": "Conversación",
   "sendOnEnter": "Enviar con Enter",
   "sendOnEnterDescription": "Enter envía (teclado virtual). Cmd/Ctrl+Enter también disponible",
+  "ttsSettings": "Texto a voz",
+  "ttsVoice": "Voz",
+  "ttsSpeechRate": "Velocidad de voz",
+  "ttsPitch": "Tono",
+  "ttsVolume": "Volumen",
+  "ttsPreview": "Vista previa de voz",
+  "ttsSystemDefault": "Predeterminado del sistema",
+  "ttsSelectVoice": "Seleccionar voz",
+  "ttsPreviewText": "Esta es una vista previa de la voz seleccionada.",
+  "ttsNoVoicesAvailable": "No hay voces disponibles",
+  "ttsVoicesForLanguage": "Voces de {language}",
+  "ttsOtherVoices": "Otros idiomas",
+  "error": "Error",
   "display": "Visualización",
   "realtime": "Tiempo real",
   "transportMode": "Modo de transporte",