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-c2-core/app/models.py

@@ -62,7 +62,12 @@ class NodeRecord(BaseModel):
     last_seen: Optional[datetime] = None
     assigned_system_id: Optional[str] = None
     node_type: str = "fixed"  # fixed or portable
-    secondary_sdr_mode: str = "none"  # none | adsb | ais | op25_2 — requires a second physical SDR
+    secondary_sdr_mode: str = "none"  # legacy single-mode field; priority[0] on current nodes
+    # Ordered decoders for the SDRs beyond op25's (node-26#9): the node runs
+    # them top-down until it runs out of dongles. Mirrored from the node's own
+    # checkin, which is the source of truth; set via PATCH /nodes/{id}.
+    secondary_sdr_priority: List[str] = []
+    secondary_sdr_running: Optional[List[str]] = None  # what the node reports actually running
     sdr_count: int = 1  # self-reported by the node's checkin, best-effort
     enforce_override_timeout: bool = True
     is_overridden: bool = False