discord_radio: desired-state streams, logout on release, no mention controls (node-26#25)

- Rewritten as RadioManager reconciling C2's retained
  nodes/{id}/discord/desired (token ids) and publishing
  nodes/{id}/discord/actual {applied_seq, sessions, streams}.
- One gateway session per leased token, one voice connection per
  (token, guild); a token no stream needs is logged OUT (client.close()),
  which is what lets C2 free it safely (item 1).
- Watchdog is a separate reconcile loop; recovering a dead session can no
  longer cancel it (item 2). Presence kept across rejoins.
- No message-content intent and no @bot leave/join mention controls (item 3).
- Local dashboard: /api/discord/join returns 409 with an explanation instead
  of a TypeError 500; /api/discord/leave pauses locally; GET /api/discord
  shows state (item 4). Join/leave results are reported to C2 (item 5).
- Token strings fetched over HTTPS from C2 (lease holder only), memory only.
- MQTT-loss fail-safe: logs every bot out after
  DISCORD_MQTT_LOSS_STOP_SECONDS (300, below C2's 600s lease grace).
- Legacy discord_join/discord_leave MQTT commands are ignored.
- Audio path unchanged: FFmpeg -f pulse on settings.pulse_source per
  connection, never Icecast.

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

drb-edge-node/app/main.py

@@ -144,20 +144,11 @@ async def on_command(payload: dict):
     action = payload.get("action")
     logger.info(f"Command received: {action}")
 
-    if action == "discord_join":
-        token = payload.get("token")
-        if not token:
-            logger.error("discord_join command missing token — ignoring.")
-            return
-        await radio_bot.join(
-            guild_id=int(payload["guild_id"]),
-            channel_id=int(payload["channel_id"]),
-            token=token,
-            call_active=metadata_watcher.is_active,
-            system_name=payload.get("system_name"),
-        )
-    elif action == "discord_leave":
-        await radio_bot.leave()
+    if action in ("discord_join", "discord_leave"):
+        # Pre-desired-state C2. Discord streams now arrive on
+        # nodes/{id}/discord/desired (node-26#25); a raw-token join is refused
+        # so a bot token is never taken from an MQTT command again.
+        logger.warning(f"Ignoring legacy {action} command — Discord radio is driven by desired state now.")
     elif action in ("set_sdr_config", "set_secondary_priority"):
         from app.internal.sdr_settings import set_sdr_settings
         try:
@@ -300,8 +291,9 @@ async def lifespan(app: FastAPI):
     mqtt_manager.on_command = on_command
     mqtt_manager.on_config_push = on_config_push
     mqtt_manager.on_api_key = on_api_key
+    mqtt_manager.on_discord_desired = radio_bot.apply_desired
 
-    # Start services (radio_bot starts on-demand when a discord_join command arrives)
+    # Start services (radio_bot starts when C2's retained discord/desired arrives)
     await mqtt_manager.connect()
     await metadata_watcher.start()
     await call_recorder.start()  # persistent PulseAudio ring buffer