fix(perimeters): report a stale WFIGS snapshot as stale, and stop serving it after a day

When WFIGS was unreachable the proxy served its last snapshot, marked stale
(X-Data-Stale, body.stale), with no age limit, and the client source kept
only the rows. The layer then read healthy with a fresh update time and
get_fire_perimeters reported the perimeters as current; three days into an
outage it still said "1 mapped wildfire perimeter in the requested box."
The source now offers getSnapshotDetail ({rows, stale, fetchedAt}); the
layer reports stale with the snapshot's fetch time, the tool adds stale,
retrieved_at and "(data may be stale)", and the proxy serves a stale
snapshot for at most 24 hours, as the GNSS proxy caps its own.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

docs/CURRENT-STATE.md

@@ -3783,7 +3783,7 @@ anchors, recovery, keyboard and mobile states; emergency repainting is covered
 by `scripts/qa-emergency-squawk.mjs`. Both accept `--timeout-ms` for slow boot.
 
 
-Fire Perimeters uses capped, timed server reads with stale-on-error caching and a per-client limit. Unchanged snapshots retain geometry; link checks cancel on disable or selection change, and the row legend shows reported containment.
+Fire Perimeters uses capped, timed server reads with stale-on-error caching and a per-client limit. A stale snapshot is served for at most 24 hours; the layer row then reads STALE, dated by that snapshot's fetch, and `get_fire_perimeters` returns `stale` and `retrieved_at` with "(data may be stale)" in its summary. Unchanged snapshots retain geometry; link checks cancel on disable or selection change, and the row legend shows reported containment.
 
 Street Level is a docked, collapsible right-rail panel (`#street-level-panel`,
 layer token `0`, option owner `street-level`, panel `ui` token `t`) that starts