Secondary SDR priority: C2 field, node command, dashboard section

Pairs with node-26 feat/secondary-sdr-priority. NodeRecord gains
secondary_sdr_priority (ordered; SDRs beyond OP25's run it top-down) and
secondary_sdr_running, both mirrored from the node's checkin.
PATCH /nodes/{id} accepts the priority, validates it, and sends it as a
'set_secondary_priority' MQTT command. A priority-only change never
re-pushes system config, because that restarts OP25. The node detail page
gets a 'Secondary SDRs' section (admin-editable) with enable, reorder,
save, and live Running / Waiting-for-SDR state from the checkin.

Verified: c2-core pytest 482 passed; frontend tsc --noEmit clean.

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

drb-frontend/app/nodes/[id]/page.tsx

@@ -8,6 +8,7 @@ import { useSystems } from "@/lib/useSystems";
 import { useCalls } from "@/lib/useCalls";
 import { StatusBadge } from "@/components/StatusBadge";
 import { NodeConfigModal } from "@/components/NodeConfigModal";
+import { SecondarySdrPriority } from "@/components/SecondarySdrPriority";
 import { CallRow } from "@/components/CallRow";
 import { MachineOutputNotice } from "@/components/ui/MachineOutputNotice";
 import { useAuth } from "@/components/AuthProvider";
@@ -336,6 +337,8 @@ export default function NodeDetailPage() {
         )}
       </div>
 
+      <SecondarySdrPriority node={node} canEdit={isAdmin} />
+
       {/* Recent calls */}
       <section>
         <h2 className="text-sm font-semibold text-gray-400 uppercase tracking-wider mb-3">Recent Calls</h2>