Pin each SDR service to a dongle by serial; OP25 always opens its SDR by serial

Fixes node-26#11. OP25's generated config said "rtl" (= whichever dongle
enumerates first), so on 2-SDR nodes a decoder could take OP25's dongle
and stop recording. Now:

- sdr_pins: {op25|adsb|ais: serial}, absent = automatic. Every OP25
  config generation (op25_client.generate_config) rewrites the device to
  rtl=<serial>: the pin, else the first dongle's serial, which is what
  "rtl" always opened. Left as "rtl" only for unknown/shared serials.
- secondary-sdr: /secondary/devices lists dongles + serials via librtlsdr
  (works while claimed). apply(priority, pins, reserved) never touches
  OP25's dongle, gives a pinned service only its own dongle, lets a
  higher-priority service take a spare from a lower one, and still runs a
  pinned lower-priority service when the top pick has no dongle.
- sdr_settings.py replaces secondary_priority.py: one apply path for the
  local dashboard, the new set_sdr_config C2 command (set_secondary_priority
  kept as an alias) and config pushes. OP25 restarts only when its own
  dongle changes. Checkin reports sdr_devices, sdr_pins, op25_sdr_serial.
- Local dashboard: 'SDRs' card with an OP25 SDR dropdown and a per-service
  dongle dropdown, duplicate-serial and double-pin warnings.

Verified: edge-node pytest 194 passed; secondary-sdr tests 7 passed;
flake8 clean; page JS passes node --check.

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

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

@@ -234,9 +234,17 @@ class MQTTManager:
             "secondary_sdr_mode": config.secondary_sdr_mode,
             "secondary_sdr_priority": config.secondary_sdr_priority,
         }
+        payload["sdr_pins"] = config.sdr_pins
         secondary = await secondary_sdr_client.status()
         if secondary is not None:
             payload["secondary_sdr_running"] = [r["mode"] for r in secondary.get("running", [])]
+            if secondary.get("devices") is not None:
+                payload["sdr_devices"] = [
+                    {k: d.get(k) for k in ("index", "serial", "name", "duplicate_serial")}
+                    for d in secondary["devices"]
+                ]
+                from app.internal.sdr_settings import op25_serial
+                payload["op25_sdr_serial"] = op25_serial(config, secondary["devices"])
         # Best-effort hardware report — omit rather than guess. Prefer the
         # secondary-sdr container's count: op25's :stable image has no lsusb and
         # its /op25/devices answers 0 rather than "unknown" when that fails. A