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/main.py

@@ -2339,6 +2339,11 @@ async def set_on_air(state: dict):
     global _show_on_air
     _show_on_air = bool(state.get("on_air", False))
     print(f"[Show] On-air: {_show_on_air}")
+    if _show_on_air:
+        _start_host_audio_sender()
+        audio_service.start_host_stream(_host_audio_sync_callback)
+    else:
+        audio_service.stop_host_stream()
     threading.Thread(target=_update_on_air_cdn, args=(_show_on_air,), daemon=True).start()
     return {"on_air": _show_on_air}
 
@@ -3285,8 +3290,6 @@ async def signalwire_audio_stream(websocket: WebSocket):
             caller_service.hangup(caller_id)
             if session.active_real_caller and session.active_real_caller.get("caller_id") == caller_id:
                 session.active_real_caller = None
-                if len(caller_service.active_calls) == 0:
-                    audio_service.stop_host_stream()
             broadcast_event("caller_disconnected", {"phone": caller_phone, "reason": disconnect_reason})
             broadcast_chat("System", f"{caller_phone} disconnected ({disconnect_reason})")
 
@@ -3394,11 +3397,6 @@ async def take_call_from_queue(caller_id: str):
         "phone": call_info["phone"],
     }
 
-    # Start host mic streaming if this is the first real caller
-    if len(caller_service.active_calls) == 1:
-        _start_host_audio_sender()
-        audio_service.start_host_stream(_host_audio_sync_callback)
-
     return {
         "status": "on_air",
         "caller": call_info,
@@ -3652,10 +3650,6 @@ async def hangup_real_caller():
     if call_sid:
         asyncio.create_task(_signalwire_end_call(call_sid))
 
-    # Stop host streaming if no more active callers
-    if len(caller_service.active_calls) == 0:
-        audio_service.stop_host_stream()
-
     session.active_real_caller = None
 
     hangup_sound = settings.sounds_dir / "hangup.wav"