feat(tts): add speech rate support for text-to-speech generation

lib/core/services/api_service.dart

@@ -1659,12 +1659,17 @@ class ApiService {
   Future<({Uint8List bytes, String mimeType})> generateSpeech({
     required String text,
     String? voice,
+    double? speed,
   }) async {
     final textPreview = text.length > 50 ? text.substring(0, 50) : text;
     _traceApi('Generating speech for text: $textPreview...');
     final response = await _dio.post(
       '/api/v1/audio/speech',
-      data: {'input': text, if (voice != null) 'voice': voice},
+      data: {
+        'input': text,
+        if (voice != null) 'voice': voice,
+        if (speed != null) 'speed': speed,
+      },
       options: Options(responseType: ResponseType.bytes),
     );
 

lib/features/chat/services/text_to_speech_service.dart

@@ -19,6 +19,7 @@ class TextToSpeechService {
   TtsEngine _engine = TtsEngine.auto;
   String? _preferredVoice;
   String? _serverPreferredVoice;
+  double _speechRate = 0.5;
   bool _initialized = false;
   bool _available = false;
   bool _voiceConfigured = false;
@@ -171,6 +172,7 @@ class TextToSpeechService {
   }) async {
     if (_initialized) {
       _engine = engine;
+      _speechRate = speechRate;
       if (deviceVoice != null) {
         _preferredVoice = deviceVoice;
         _voiceConfigured = false;
@@ -183,6 +185,7 @@ class TextToSpeechService {
     }
 
     _engine = engine;
+    _speechRate = speechRate;
     _preferredVoice = deviceVoice;
     _serverPreferredVoice = serverVoice;
     _voiceConfigured = false;
@@ -352,6 +355,7 @@ class TextToSpeechService {
       if (engine != null) _engine = engine;
       if (voiceProvided) _preferredVoice = voiceValue;
       if (serverVoiceProvided) _serverPreferredVoice = serverVoiceValue;
+      if (speechRate != null) _speechRate = speechRate;
       return;
     }
 
@@ -369,6 +373,7 @@ class TextToSpeechService {
         await _tts.setVolume(volume);
       }
       if (speechRate != null) {
+        _speechRate = speechRate;
         await _tts.setSpeechRate(speechRate);
       }
       if (pitch != null) {
@@ -645,7 +650,11 @@ class TextToSpeechService {
     String? voice,
     int session,
   ) async {
-    return await _api!.generateSpeech(text: text, voice: voice);
+    return await _api!.generateSpeech(
+      text: text,
+      voice: voice,
+      speed: _speechRate,
+    );
   }
 
   Future<void> _onAudioComplete() async {

lib/features/profile/views/app_customization_page.dart

@@ -944,7 +944,7 @@ class AppCustomizationPage extends ConsumerWidget {
                 value: settings.ttsSpeechRate,
                 min: 0.25,
                 max: 2.0,
-                divisions: 7,
+                divisions: 35,
                 label: '${(settings.ttsSpeechRate * 100).round()}%',
                 onChanged: (value) => ref
                     .read(appSettingsProvider.notifier)