compose: opt-in trunk-recorder service + supervisor and uploadScript (node-26#45)

robotastic/trunk-recorder:5.2.1 pinned by digest, behind the
trunk-recorder compose profile, host network, /dev/bus/usb. run.sh
restarts TR when the edge-node rewrites config.json and reports state
for health; drb-upload.sh hands each finished call (wav, then json) to
recordings/tr-inbox. README carries the GPL-3.0 source note.

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

.env.example

@@ -108,6 +108,23 @@ UPLOAD_SPOOL_MAX_AGE_HOURS=72
 UPLOAD_RETRY_MIN_SECONDS=15
 UPLOAD_RETRY_MAX_SECONDS=600
 
+# --- Recorder backend (node-26#45) -------------------------------------------
+# op25 (default): OP25 + PulseAudio recorder, one call at a time.
+# trunk-recorder: Trunk Recorder records every talkgroup at once, with call
+# boundaries from the decoder. Set BOTH lines below to switch; OP25 is then
+# never started (it would hold the SDR), and the live browser stream (Icecast)
+# goes quiet — Discord live audio keeps working.
+RECORDER_BACKEND=op25
+# COMPOSE_PROFILES=trunk-recorder
+# Trunk Recorder SDR settings (only read with RECORDER_BACKEND=trunk-recorder).
+# TR_SAMPLE_RATE=2400000
+# TR_GAIN=34
+# TR_CENTER_HZ=            # override the computed centre frequency
+# TR_DIGITAL_RECORDERS=4   # simultaneous voice channels on a trunked system
+# TR_MIN_DURATION=1.0      # seconds; shorter calls are dropped by TR
+# TR_SQUELCH_DB=-50        # conventional channels; absolute dB, tune per site
+# TR_LIVE_PORT=9123        # local UDP port for simplestream -> Discord
+
 # OP25 container (usually no need to change)
 OP25_API_URL=http://localhost:8001
 OP25_TERMINAL_URL=http://localhost:8081