Adds io.lotus.inject_audio (toWidget): mixes a soundboard clip into the
call so other participants hear it. Publishes the clip as a separate
Unknown-source LiveKit track (rendered by MatrixAudioRenderer) rather than
splicing into the mic track, so the denoise pipeline is untouched; the
track is unpublished when the clip ends (with a 30s safety cap). This is
the real call-audio injection that was impossible against the prebuilt EC
bundle. Additive: no-op unless the host sends the action.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
