feat(layers): add shipwrecks layer (EMODnet + Wikidata)

A new Events layer maps shipwrecks with a card per wreck:
- EMODnet Human Activities heritage shipwrecks (about 6,500 in European
  waters, CC BY 4.0), skipping rows taken from wrecksite.eu.
- Wikidata shipwrecks with a Wikipedia article plus sinking events
  (CC0); an event folds into its ship for the date and death toll.
- A same-origin /api/shipwrecks proxy refreshes once a day and serves
  the last snapshot as stale for up to a week.

Markers are a boat icon coloured by era and sized by deaths; four era
chips filter the layer. The card follows the air-accidents layout
(deaths first). Text that names people is dropped; victims appear as
a count only.

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

src/data/layerStateTokenReservations.json

@@ -24,6 +24,7 @@
   ["s2-ghostmaps", "5"],
   ["satellites", "s"],
   ["sea-marks", "6"],
+  ["shipwrecks", "9"],
   ["ski-pistes", "7"],
   ["street-level", "0"],
   ["telegeography-submarine-cables", "u"],