edge-node: Trunk Recorder backend behind RECORDER_BACKEND (node-26#45)

RECORDER_BACKEND=trunk-recorder (default op25, unchanged):
- tr_config: TR config.json + talkgroup/channel CSVs from the C2 system
  config (P25 trunked, P25 conventional, analog with squelch).
- tr_calls: TR call JSON -> MQTT call_start/call_end + /upload fields
  (talkgroup, start/stop, freq, units from srcList, emergency, encrypted).
- trunk_recorder: inbox ingest through the #44 spool with deterministic
  call_ids, supervisor requests, live audio via simplestream -> pacat ->
  drb_sink for Discord (one talkgroup at a time).
- radio_backend: start/stop dispatch so OP25 never grabs the SDR, and the
  OP25 watcher/PulseAudio recorder stay off (no double uploads).
- health/dashboard/checkin show the active backend and TR health.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

drb-edge-node/app/internal/mqtt_manager.py

@@ -419,6 +419,14 @@ class MQTTManager:
         last = spool["last_result"] or {}
         payload["last_upload_status"] = last.get("status")
         payload["last_upload_kind"] = last.get("kind")
+        # node-26#45: which recorder this node runs; C2 ignores unknown keys.
+        payload["recorder_backend"] = settings.recorder_backend
+        from app.internal import trunk_recorder as tr
+        if tr.enabled():
+            facts = tr.trunk_recorder.health_facts()
+            payload["tr_state"] = (facts["status"] or {}).get("state")
+            payload["tr_decode_rate"] = facts["decode_rate"]
+            payload["tr_inbox_backlog"] = facts["inbox_backlog"]
         self._publish(self._t_checkin, payload, qos=1)
 
     def _publish(self, topic: str, payload: dict, qos: int = 0, retain: bool = False):