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by MatrixAudioRenderer) rather than splicing into the mic track, so the denoise pipeline is untouched; the track is unpublished when the clip ends (with a 30s safety cap).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>