feat: Wildlife Sightings layer from iNaturalist and Acartia

Recent community wildlife observations, as a new Wildlife group in the
layer panel.

- Server: keyless iNaturalist proxy (v2 observations with only the
  projected fields; undocumented v1 UTFGrid density tiles, decoded on the
  server) sharing one paced queue (burst 4, ~1/s, 60/min, 8,000/day budget,
  up to four in flight), in-memory caches and upstream-only cooldowns;
  Acartia Salish Sea marine-mammal feed rounded to 0.01 degrees with
  comments dropped.
- Layer: grid counts drawn as a soft view-ranked density glow; real sampled
  sightings as taxon badges at their true positions with ambient photo
  thumbnails and labels; obscured records stay privacy cells; a clicked
  sighting stays pinned through camera moves and refreshes.
- Anchored photo card per selection with the single iNaturalist link;
  attribution in the layer row and the Data attribution popover.
- Filters (CONFIRMED, taxa presets) round-trip in share links with token 9.

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

src/app/sourceComposition.js

@@ -50,6 +50,7 @@ export const CATALOG_SOURCE_CONTRACTS = Object.freeze({
   'gnss-integrity': contract(['gnss-integrity'], ['getSnapshot']),
   's2-ghostmaps': contract(['s2-ghostmaps'], ['getCatalog', 'getFile']),
   'drone-airspace': contract(['drone-airspace'], ['getSnapshot']),
+  'wildlife-sightings': contract(['wildlife-sightings'], ['getSnapshot']),
   cables: contract(['telegeography-submarine-cables'], ['fetch']),
   transit: contract(['transit'], ['requestSnapshot', 'getHistory']),
 });