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/app/sourceComposition.js

@@ -49,6 +49,7 @@ export const CATALOG_SOURCE_CONTRACTS = Object.freeze({
   'air-quality': contract(['air-quality'], ['getSnapshot']),
   'gnss-integrity': contract(['gnss-integrity'], ['getSnapshot']),
   's2-ghostmaps': contract(['s2-ghostmaps'], ['getCatalog', 'getFile']),
+  shipwrecks: contract(['shipwrecks'], ['getSnapshot']),
   'drone-airspace': contract(['drone-airspace'], ['getSnapshot']),
   cables: contract(['telegeography-submarine-cables'], ['fetch']),
   transit: contract(['transit'], ['requestSnapshot', 'getHistory']),