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/api/hermes/tts.ts

@@ -1,6 +1,8 @@
 export interface TtsOptions {
   text: string
   lang?: string
+  rate?: string   // Edge TTS rate format: "+NN%" or "-NN%"
+  pitch?: string  // Edge TTS pitch format: "+NNHz" or "-NNHz"
 }
 
 export async function generateSpeech(opts: TtsOptions): Promise<{ audio: Blob; engine: string }> {