Changelog entries now have their own page

Until now, /changelog rendered every update's full text on one long page. There was no page of its own for a single entry, so a link meant to point at one specific update, from the RSS feed, from /llms.txt, or from another changelog entry referencing a later follow-up, led nowhere real.

Each update now has its own page at /changelog/<slug>. The /changelog list itself is now a paginated set of cards, 20 per page: a screenshot (or a placeholder graphic for updates that don't have one) on the left, the date, a type badge, a short summary, and a "Read more" button that opens the full entry. Clicking a card's screenshot zooms it in a modal instead of navigating away; on the entry's own page, the same screenshot shows uncropped at its full size below the text.

If you had a link to a specific update bookmarked from before, update it: the old /changelog#<anchor> links no longer resolve to that entry now that the list doesn't render full entries inline.