Add whisper_stt CLI with default diarization, Ubuntu README, editor config

- Replace test.py with whisper_stt.py: OpenAI Whisper + default speaker diarization
  via local ./models/pyannote-diarization-3.1; --no-diarize for plain text
- Add requirements-whisper-stt.txt (whisper, pyannote, huggingface_hub, imageio-ffmpeg)
- README: stt conda env, Ubuntu/macOS ffmpeg, CLI usage
- .vscode: Python interpreter /opt/anaconda3/envs/stt; .cursor rule for stt env
- .gitignore: exclude downloaded pyannote snapshot under models/

Made-with: Cursor

.vscode/settings.json

@@ -0,0 +1,5 @@
+{
+  "python.defaultInterpreterPath": "/opt/anaconda3/envs/stt/bin/python",
+  "python.condaPath": "/opt/anaconda3/bin/conda",
+  "python.terminal.activateEnvironment": true
+}