Live ops wall + pluggable camera providers with licence gating (server-26#198)

Backend (c2-core):
- app/internal/cameras/: provider interface, licence model, per-provider
  catalog cache; one adapter per source in design-canvas/camera-sources.md.
  Implemented: 511NY (legacy shape + tolerant XML inventory parser, 511x
  endpoints UNVERIFIED), Caltrans, DelDOT, Ontario 511, DriveBC, Calgary,
  TfL, NSW, Fintraffic. Stubs: NYC DOT, Westchester DPW, TRANSCOM, CTroads,
  511NJ, Austin, TxDOT, MD CHART, WSDOT, Tallinn, Tarktee, Warendorf,
  TrafficLand, Windy, EarthCam.
- Every provider defaults OFF (config/camera_providers). Gated licences
  (agreement required / unverified / non-commercial / paid) need an explicit
  acknowledgement stored with who/when and written to audit_log; the audit
  write is a precondition. Stubs and prohibited sources cannot be enabled.
  Ack is bound to the licence status it was given for.
- GET /cameras (signed-in), GET/PUT /admin/camera-providers (admin only).
- /traffic/511 follows the ny511 provider switch and returns the DAA credit
  + NYSDOT as-is disclaimer; 511NY event descriptions no longer truncated
  ("may not alter the substance of a report").

Frontend:
- LiveView becomes the ops wall: Region > Incident > Camera drill-down,
  worst-first rail (MapView), KPIs, transcript ticker, scrubber incident
  bands, auto-tour, deep links (#inc=&cam=&tour), Esc steps up.
- Incident panel: nearest cameras (path-weighted), fused situational context
  (ADS-B, AIS, 511NY events, NEXRAD tile sample), units, call spine.
- MapView keeps every layer; adds Camera Viewsheds (approx.) overlay and a
  nearest-camera layer for the selected incident.
- CameraFeed hygiene: hidden-tab/off-screen gating, 2 concurrent HLS cap,
  last good frame + stale badge, frozen-frame signature, HLS stall watchdog,
  provider attribution rendered on the imagery.
- Camera/event popups show source credit, update time and the disclaimer.
- Admin > Camera providers tab with licence status, health, gated confirm.
- Camera detection is not built (blocked on #199/#200); seam only.

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

drb-frontend/lib/useCameras.ts

@@ -0,0 +1,81 @@
+"use client";
+
+import { useEffect, useRef, useState } from "react";
+import type L from "leaflet";
+import { c2api } from "@/lib/c2api";
+import type { CamerasResponse } from "@/lib/types";
+
+// Public cameras from every provider an admin has enabled (GET /cameras).
+// Catalogs are cached server-side (15 min); this only re-asks for the bbox.
+const POLL_MS = 5 * 60 * 1000;
+const MOVE_DEBOUNCE_MS = 400;
+const BBOX_PAD = 0.2;
+
+export interface BBox { south: number; west: number; north: number; east: number }
+
+const EMPTY: CamerasResponse = { cameras: [], providers: [], serving_count: 0 };
+
+function useCameraFetch(getBox: (() => BBox | null) | null, deps: unknown[], subscribe?: (reload: () => void) => () => void) {
+  const [data, setData] = useState<CamerasResponse>(EMPTY);
+  const [error, setError] = useState<string | null>(null);
+  const [loaded, setLoaded] = useState(false);
+  const seq = useRef(0);
+
+  useEffect(() => {
+    if (!getBox) { setData(EMPTY); setLoaded(false); return; }
+    const boxFn = getBox;
+    const load = async () => {
+      const box = boxFn();
+      if (!box) return;
+      const mine = ++seq.current;
+      try {
+        const res = await c2api.getCameras(box);
+        if (mine !== seq.current) return;
+        setData(res);
+        setError(null);
+        setLoaded(true);
+      } catch (e) {
+        if (mine !== seq.current) return;
+        console.error("useCameras:", e);
+        setError(e instanceof Error ? e.message : String(e));
+        setLoaded(true);
+      }
+    };
+    load();
+    const unsub = subscribe ? subscribe(load) : undefined;
+    const poll = setInterval(() => { if (!document.hidden) load(); }, POLL_MS);
+    return () => {
+      unsub?.();
+      clearInterval(poll);
+      seq.current++;
+    };
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, deps);
+
+  return { data, error, loaded };
+}
+
+/** Cameras for the current map view, refetched on pan/zoom while `enabled`. */
+export function useMapCameras(map: L.Map, enabled: boolean) {
+  return useCameraFetch(
+    enabled
+      ? () => {
+          const b = map.getBounds().pad(BBOX_PAD);
+          return { south: b.getSouth(), west: b.getWest(), north: b.getNorth(), east: b.getEast() };
+        }
+      : null,
+    [map, enabled],
+    (reload) => {
+      let t: ReturnType<typeof setTimeout> | undefined;
+      const onMove = () => { clearTimeout(t); t = setTimeout(reload, MOVE_DEBOUNCE_MS); };
+      map.on("moveend", onMove);
+      return () => { map.off("moveend", onMove); clearTimeout(t); };
+    },
+  );
+}
+
+/** Cameras inside a fixed bbox (e.g. around the active incidents). `null` = don't fetch. */
+export function useCamerasInBbox(box: BBox | null) {
+  const key = box ? `${box.south.toFixed(3)},${box.west.toFixed(3)},${box.north.toFixed(3)},${box.east.toFixed(3)}` : "";
+  return useCameraFetch(box ? () => box : null, [key]);
+}