faster_whisper_backend: VadOptions `threshold` param renamed to `onset` in faster-whisper 1.1.0

## Bug `faster_whisper_backend.py` line 79 sets: ```python self.vad_parameters = vad_parameters or {"threshold": 0.5} ``` But `faster-whisper==1.1.0` (which is pinned in `setup.py`) renamed `VadOptions.threshold` to `VadOptions.onset`. This causes every transcription attempt to fail with: ``` VadOptions.__init__() got an unexpected keyword argument 'threshold' ``` The error repeats on every audio chunk, so no transcription output is ever produced. ## Fix Change `"threshold"` to `"onset"`: ```python self.vad_parameters = vad_parameters or {"onset": 0.5} ``` ## Steps to reproduce ```bash pip install whisper-live # installs faster-whisper==1.1.0 python3 run_server.py --port 9090 --backend faster_whisper # connect any client — server logs the error on every audio chunk ```