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>

src/routes/+page.svelte

@@ -133,6 +133,7 @@
         device: $settings.transcription_device || undefined,
         language: $settings.transcription_language || undefined,
         skipDiarization: $settings.skip_diarization || undefined,
+        hfToken: $settings.hf_token || undefined,
       });
 
       // Create speaker entries from pipeline result