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-c2-core/app/routers/traffic.py

@@ -0,0 +1,38 @@
+import asyncio
+from typing import Optional
+
+from fastapi import APIRouter, HTTPException, Query
+
+from app.internal import ny511
+
+router = APIRouter(prefix="/traffic", tags=["traffic"])
+
+# Per-layer cap per response. A statewide view is ~3k cameras; past this the
+# map is unreadable anyway, and the client is told the list was cut.
+MAX_ITEMS = 1500
+
+
+def _feed_status(feed: "ny511._Feed") -> dict:
+    return {"fetched_at": feed.fetched_at, "error": feed.error}
+
+
+@router.get("/511")
+async def get_511(
+    south: float = Query(..., ge=-90, le=90),
+    west: float = Query(..., ge=-180, le=180),
+    north: float = Query(..., ge=-90, le=90),
+    east: float = Query(..., ge=-180, le=180),
+    layers: Optional[str] = Query("cameras,events", description="comma list: cameras, events"),
+):
+    if south > north or west > east:
+        raise HTTPException(400, "bbox must satisfy south<=north and west<=east")
+    wanted = {s.strip() for s in (layers or "").split(",") if s.strip()}
+    feeds = {name: getattr(ny511, name) for name in ("cameras", "events") if name in wanted}
+    await asyncio.gather(*(f.get() for f in feeds.values()))
+
+    out: dict = {}
+    for name, feed in feeds.items():
+        hits = ny511.in_bbox(feed.items, south, west, north, east)
+        out[name] = hits[:MAX_ITEMS]
+        out[f"{name}_status"] = {**_feed_status(feed), "total_in_bbox": len(hits), "truncated": len(hits) > MAX_ITEMS}
+    return out