Web STT: speaker diarization via pyannote; whisper_stt snapshot validation

- Add app/diarize.py: merge faster-whisper segments with pyannote (A/B/C)
- Wire /api/jobs and /api/transcribe; job API returns speaker_diarization, diarize_skip_reason
- UI: meta line shows diarization applied/skipped; hint for models path
- requirements.txt: pyannote.audio; README APP_DIARIZE / APP_PYANNOTE_MODEL_DIR
- whisper_stt.py: validate config.yaml before loading pipeline
- requirements-whisper-stt.txt: minor doc updates if any

Made-with: Cursor

requirements.txt

@@ -4,5 +4,6 @@ python-multipart
 pydantic
 faster-whisper
 imageio-ffmpeg
+pyannote.audio>=3.1.0
 psycopg[binary]
 python-dotenv