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_nl.arb

@@ -309,6 +309,19 @@
   "chatSettings": "Chat",
   "sendOnEnter": "Verzenden met Enter",
   "sendOnEnterDescription": "Enter verzendt (softtoetsenbord). Cmd/Ctrl+Enter ook beschikbaar",
+  "ttsSettings": "Tekst naar spraak",
+  "ttsVoice": "Stem",
+  "ttsSpeechRate": "Spraaksnelheid",
+  "ttsPitch": "Toonhoogte",
+  "ttsVolume": "Volume",
+  "ttsPreview": "Stemvoorbeeld",
+  "ttsSystemDefault": "Systeemstandaard",
+  "ttsSelectVoice": "Selecteer stem",
+  "ttsPreviewText": "Dit is een voorbeeld van de geselecteerde stem.",
+  "ttsNoVoicesAvailable": "Geen stemmen beschikbaar",
+  "ttsVoicesForLanguage": "{language} stemmen",
+  "ttsOtherVoices": "Andere talen",
+  "error": "Fout",
   "display": "Weergave",
   "realtime": "Realtime",
   "transportMode": "Transportmodus",