Add HuggingFace token setting for speaker detection

- Add "Speakers" tab in Settings with HF token input field
- Include step-by-step instructions for obtaining the token
- Pass hf_token from settings through Rust → Python pipeline → diarize
- Token can also be set via HF_TOKEN environment variable as fallback
- Move skip_diarization checkbox to Speakers tab

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

python/voice_to_notes/ipc/handlers.py

@@ -107,6 +107,7 @@ def make_pipeline_handler() -> HandlerFunc:
             min_speakers=payload.get("min_speakers"),
             max_speakers=payload.get("max_speakers"),
             skip_diarization=payload.get("skip_diarization", False),
+            hf_token=payload.get("hf_token"),
         )
         return IPCMessage(
             id=msg.id,