feat: add Edge TTS rate/pitch sliders to voice settings (#629)

Add speed (rate) and pitch controls for Edge TTS provider:
- Frontend: speedToEdgeRate()/hzToEdgePitch() helpers + UI sliders
- Backend: rate/pitch passthrough in OpenaiTtsRequest and controller
- i18n: add edgeRate/edgePitch keys across all 8 languages
- Rate: 0.5x-2.0x slider, Pitch: -20Hz to +20Hz slider

packages/client/src/i18n/locales/en.ts

@@ -793,6 +793,11 @@ export default {
       edgeUrlPlaceholder: 'http://127.0.0.1:9882',
       edgeVoice: 'Voice',
       edgeVoiceHint: 'Select a voice for speech synthesis',
+      edgeRate: 'Speed',
+      edgeRateHint: 'Adjust speech speed (0.5x ~ 2.0x)',
+      edgePitch: 'Pitch',
+      edgePitchHint: 'Adjust speech pitch (-20 ~ +20 Hz)',
+
 
       // Test
       testTitle: 'Test Voice',