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_fr.arb

@@ -316,6 +316,19 @@
   "chatSettings": "Discussion",
   "sendOnEnter": "Envoyer avec Entrée",
   "sendOnEnterDescription": "Entrée envoie (clavier logiciel). Cmd/Ctrl+Entrée aussi disponible",
+  "ttsSettings": "Synthèse vocale",
+  "ttsVoice": "Voix",
+  "ttsSpeechRate": "Vitesse de parole",
+  "ttsPitch": "Hauteur",
+  "ttsVolume": "Volume",
+  "ttsPreview": "Aperçu de la voix",
+  "ttsSystemDefault": "Système par défaut",
+  "ttsSelectVoice": "Sélectionner la voix",
+  "ttsPreviewText": "Ceci est un aperçu de la voix sélectionnée.",
+  "ttsNoVoicesAvailable": "Aucune voix disponible",
+  "ttsVoicesForLanguage": "Voix {language}",
+  "ttsOtherVoices": "Autres langues",
+  "error": "Erreur",
   "display": "Affichage",
   "realtime": "Temps réel",
   "transportMode": "Mode de transport",