/api/audio/speak-stream WebSocket: one socket + one Web Audio clock per
reply. The renderer feeds raw LLM deltas as they arrive; the server
cuts sentences with the shared chunker and streams int16 PCM back while
generation continues — speech overlaps generation with no per-sentence
connection or synthesis gaps. Falls back to the POST data-URL path for
old backends / non-chunked providers.
Barge-in runs a MediaRecorder on the monitor's stream the whole time
playback is live (rotated while quiet to bound pre-roll); talking over
the agent cuts playback and the complete utterance goes straight to
transcription and submit. /api/audio/transcribe returns 200/"" for
no-speech results so quiet turns re-listen instead of toasting a 400.
