fix(shipwrecks): the page clears shown wrecks as a whole, once even the newest source is too old

Removing one source's wrecks on the page split merged records: a wreck both
sources list is one Wikidata record carrying EMODnet facts, so expiring
Wikidata dropped wrecks EMODnet still had, and expiring EMODnet kept its
facts. The page now keeps every shown wreck, marked stale, until the newest
source passes the limit, then clears them all. Adds a source test for the
reported ages and limit.

docs/CURRENT-STATE.md

@@ -164,9 +164,10 @@ one that failed is asked again after 15 minutes. Each source keeps its own last
 good records: a source that fails, answers with nothing usable, or answers with
 less than half of its last good set keeps serving its earlier records as stale
 for up to seven days, and never removes the other source's wrecks. When the
-page cannot refresh, the wrecks it shows are marked stale, and it removes each
-source's wrecks once they pass seven days, counted from the age the proxy
-reported (so the page and server clocks are never compared). EMODnet rows the portal took from
+page cannot refresh, the wrecks it shows are marked stale, and it removes them
+once even the newest source is past seven days, counted from the ages the
+proxy reported (so the page and server clocks are never compared; a wreck
+both sources list is one record, so nothing is removed per source). EMODnet rows the portal took from
 wrecksite.eu are skipped (that site is not openly licensed). A Wikidata wreck
 with the same name within 3 km of an EMODnet wreck is merged into one record
 that keeps the article link and takes EMODnet's year, sinking text, depth and