WebRTC audio mirror: AAC cannot cross WebRTC, so transcode audio to Opus into <path>.webrtc

bin/mtx-on-ready.sh (runOnReady inside the mediamtx container) posts the is-live notice and, for sources whose
audio is not Opus, runs ffmpeg: video copy, audio -> Opus, published over MediaMTX's loopback RTSP to
<user>/<Title>.webrtc (record: no). dumpd accepts .webrtc publishes only from 127.0.0.1. The portal hides
mirror paths, plays the mirror over WHEP (HLS stays on the source), holds an AAC source for 15 s while its
mirror comes up, and corrects the viewer count. Verified headless with a mocked path list.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

docker-compose.yml

@@ -17,6 +17,7 @@ services:
       - "127.0.0.1:9997:9997"    # API      -> Caddy live.HOST/api/*
     volumes:
       - ./mediamtx.yml:/mediamtx.yml:ro
+      - ./bin/mtx-on-ready.sh:/vanguard/on-ready.sh:ro   # is-live notice + WebRTC audio mirror (runOnReady)
       - /srv/media/streams:/recordings
     restart: unless-stopped