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/secondary_sdr_client.py

@@ -15,12 +15,25 @@ class SecondarySdrClient:
     def __init__(self):
         self.api_url = settings.secondary_sdr_api_url
 
-    async def apply(self, priority: List[str]) -> Optional[List[str]]:
-        """Run decoders down the priority list until SDRs run out. Returns the
-        modes actually running, or None if the container is unreachable."""
+    async def devices(self) -> Optional[List[Dict[str, Any]]]:
+        """Every RTL-SDR on the node with its serial, or None if unreachable."""
+        try:
+            async with httpx.AsyncClient(timeout=5) as client:
+                r = await client.get(f"{self.api_url}/secondary/devices")
+                r.raise_for_status()
+                return r.json().get("devices", [])
+        except Exception as e:
+            logger.error(f"Secondary SDR device list failed: {e}")
+            return None
+
+    async def apply(self, priority: List[str], pins: Dict[str, str], reserved: List[str]) -> Optional[List[str]]:
+        """Run decoders down the priority list until SDRs run out, honouring
+        pins and never touching `reserved` (op25's) dongles. Returns the modes
+        actually running, or None if the container is unreachable."""
+        body = {"priority": priority, "pins": pins, "reserved": reserved}
         try:
             async with httpx.AsyncClient(timeout=30) as client:
-                r = await client.post(f"{self.api_url}/secondary/apply", json={"priority": priority})
+                r = await client.post(f"{self.api_url}/secondary/apply", json=body)
                 r.raise_for_status()
                 return r.json().get("running", [])
         except Exception as e: