511NY DOT cameras + traffic events map layers (#183)

GET /traffic/511 serves a bbox slice of the statewide 511NY camera and event
feeds from an in-memory cache (cameras 1h, events 2m TTL, fetched lazily) --
public data, so no Firestore writes. A failed refresh keeps the last good data
and reports the error; a schema change (nothing parses) is an error, not an
empty layer. Frontend: opt-in "DOT Cameras" and "Traffic Events" overlays that
fetch only while shown, with an on-map notice when the feed is down or stale.
NY511_API_KEY is optional in config (the API answers without one today; the
terms require a registered key).

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

drb-frontend/lib/types.ts

@@ -98,6 +98,49 @@ export interface VesselTrack {
   last_seen: string;
 }
 
+// 511NY traffic layer (server-26#183) — GET /traffic/511, cached server-side,
+// not Firestore. *_local times are New York local, no offset: display only.
+export interface Ny511Camera {
+  id: string;
+  lat: number;
+  lon: number;
+  name: string;
+  roadway: string;
+  direction: string;
+  image_url: string | null;
+  video_url: string | null;
+}
+
+export interface Ny511Event {
+  id: string;
+  lat: number;
+  lon: number;
+  type: string;
+  subtype: string;
+  severity: string;
+  roadway: string;
+  direction: string;
+  county: string;
+  description: string;
+  start_local: string | null;
+  planned_end_local: string | null;
+  updated_local: string | null;
+}
+
+export interface Ny511FeedStatus {
+  fetched_at: number | null;  // epoch seconds of the last successful 511NY fetch
+  error: string | null;       // set when the latest refresh failed (data is then stale)
+  total_in_bbox: number;
+  truncated: boolean;
+}
+
+export interface Ny511Response {
+  cameras?: Ny511Camera[];
+  cameras_status?: Ny511FeedStatus;
+  events?: Ny511Event[];
+  events_status?: Ny511FeedStatus;
+}
+
 export interface VocabularyPendingTerm {
   term: string;
   source: "induction" | "correction";