Node SDRs: pin OP25 and each service to a dongle by serial (node-26#11)

Pairs with node-26 feat/sdr-pins. NodeRecord gains sdr_pins
(service -> serial), sdr_devices and op25_sdr_serial, mirrored from the
node's checkin. PATCH /nodes/{id} validates pins (known services, one
dongle per service) and sends priority/pins as a 'set_sdr_config'
command, never a config re-push. The node restarts OP25 only when OP25's
own dongle changes. The node page's section becomes 'SDRs' with an OP25
SDR dropdown ('Automatic (first SDR)' + detected dongles) and a
per-service dongle dropdown ('Any spare SDR'), plus duplicate-serial and
double-pin warnings.

Verified: c2-core pytest 490 passed; frontend tsc --noEmit clean.

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

drb-frontend/lib/c2api.ts

@@ -37,7 +37,12 @@ export const c2api = {
     request(`/nodes/${nodeId}/override/reset`, { method: "POST" }),
   updateNode: (
     id: string,
-    body: { node_type?: string; enforce_override_timeout?: boolean; secondary_sdr_priority?: string[] },
+    body: {
+      node_type?: string;
+      enforce_override_timeout?: boolean;
+      secondary_sdr_priority?: string[];
+      sdr_pins?: Record<string, string | null>;
+    },
   ) =>
     request(`/nodes/${id}`, { method: "PATCH", body: JSON.stringify(body) }),