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]>

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