Add speaker-labeled transcripts, favicon, host stream fix, episode page

- Re-label all 8 episode transcripts with LUKE:/CALLER: speaker labels
  using LLM-based diarization (relabel_transcripts.py)
- Add episode.html transcript page with styled speaker labels
- Update publish_episode.py to generate speaker-labeled transcripts
  and copy to website/transcripts/ for Cloudflare Pages
- Add SVG favicon with PNG fallbacks
- Fix CPU issue: tie host audio stream to on-air toggle, not per-caller
- Update how-it-works page with post-production pipeline info
- Add transcript links to episode cards in app.js

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

backend/services/audio.py

@@ -515,6 +515,9 @@ class AudioService:
 
     def start_host_stream(self, send_callback: Callable):
         """Start continuous host mic capture for streaming to real callers"""
+        if self._host_stream is not None:
+            self._host_send_callback = send_callback
+            return
         if self.input_device is None:
             print("[Audio] No input device configured for host streaming")
             return