New coastal listings

Listings are ordered by the most trustworthy date each source actually provides: a source-reported freshness date where a feed supplies one, falling back to the date Costaia first ingested the listing where it doesn't.

This is never based on when a listing was last touched internally or on sync timing -- only on real, source-anchored signals, the same ordering used everywhere else on Costaia that claims to show "newest" listings.

Not every source reports a per-listing date with the same precision, so "new" is a best-available signal per source rather than a single guaranteed timestamp across all of them.