Drive call boundaries from audio, use the console only for the label

The control channel was wrong in both directions. Grants fire 0.84-1.62s
before anyone speaks, and srcaddr can drop to 0 while someone is still
talking - one recording came back "-1.61s lead, -0.00s tail", the trim
finding nothing to remove because the window had closed on live speech.
Confirmed by ear: the cut lands at a word boundary on an unfinished word.

Audio is ground truth for WHEN. The console remains the only source of
WHO, so it still supplies talkgroup, alias and rid.

  START  voice onset in the captured audio, with a 0.25s pre-roll that
         now covers only chunk quantisation and threshold ramp-up rather
         than a variable control-channel offset.
  STOP   call_silence_timeout seconds of silence heard in the audio.
  LABEL  resolved AT CLOSE from a bounded rolling history of console
         observations overlapping the window, +4s/-2s, because there is
         no guaranteed ordering between a grant and its audio.
  SPLIT  a console talkgroup change still forces a cut, since two calls
         with no silence between them would otherwise merge into one.

Capture now emits raw PCM instead of MP3. Silence detection becomes
integer arithmetic per chunk with no decode, trimming becomes a byte
offset slice rather than a second ffmpeg pass, and MP3 encoding happens
exactly once at save - uploads are no longer double-encoded.

Audio with no talkgroup anywhere in its window is discarded rather than
uploaded: an untagged call silently poisons incident correlation, which
is worse than losing the audio. Logged at ERROR and counted on
/api/status.

When capture produces no audio at all the old console state machine
still runs, so a node with a broken audio path keeps reporting radio
activity. That is now the only consumer of call_idle_timeout.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

drb-edge-node/app/routers/api.py

@@ -49,9 +49,16 @@ async def get_status():
         "system_name": system_name,
         "is_recording": call_recorder.is_recording,
         # Health of the PulseAudio capture that feeds every recording — the single
-        # most useful signal when recordings come back empty.
+        # most useful signal when recordings come back empty. Segment boundaries
+        # come from this stream, so audio_silence_seconds is also how far the
+        # node currently is from closing whatever it is recording.
         "audio_capture": call_recorder.is_capturing,
         "buffered_seconds": round(call_recorder.buffered_seconds, 1),
+        "audio_silence_seconds": round(call_recorder.audio_activity().silence_seconds, 1),
+        # Audio that was recorded but had no OP25 talkgroup anywhere near it, so
+        # it was discarded rather than uploaded. Non-zero means either the
+        # console is not decoding or something else is feeding drb_sink.
+        "unattributed_segments": metadata_watcher.unattributed_segments,
         "active_tgid": active_tgid,
         "active_tgid_name": active_tgid_name,
         "active_call_id": metadata_watcher.active_call_id,