[Qwen3TTS][ServingSpeech] Bugfix/voice upload and add optional ref_text (#2046)

Signed-off-by: JuanPZuluaga <juanz9312@gmail.com>
Co-authored-by: Yueqian Lin <70319226+linyueqian@users.noreply.github.com>

docs/user_guide/examples/online_serving/qwen3_tts.md

@@ -242,6 +242,7 @@ Upload a new voice sample for voice cloning in Base task TTS requests.
 - `audio_sample` (required): Audio file (max 10MB, supported formats: wav, mp3, flac, ogg, aac, webm, mp4)
 - `consent` (required): Consent recording ID
 - `name` (required): Name for the new voice
+- `ref_text` (optional): Transcript of the audio. Enables in-context voice cloning (higher quality).
 
 **Response Example:**
 ```json
@@ -262,7 +263,8 @@ Upload a new voice sample for voice cloning in Base task TTS requests.
 curl -X POST http://localhost:8000/v1/audio/voices \
   -F "audio_sample=@/path/to/voice_sample.wav" \
   -F "consent=user_consent_id" \
-  -F "name=custom_voice_1"
+  -F "name=custom_voice_1" \
+  -F "ref_text=The exact transcript of the audio sample."
 ```
 
 ### Endpoint