Return a compact public log of recently updated Atlas pages.

This is purposefully a current-page activity stream: one row per active, PUBLISHED pillar ordered by its real editorial-event timestamp — the LATER of the latest TagPillarRevision.created_at (if any) and published_at. A pillar's first revision can PREDATE its publish date: create_reviewed_pillar writes a "[create draft]" baseline TagPillarRevision on drafts, and publish_tag_pillars stamps published_at afterward with no revision of its own. So a revision row alone does not mean "corrected after publish" — only a revision at or after published_at does; otherwise the row is a first publication. Drafts, public stubs, revision bodies, citation lists, and non-public snapshots never enter this response.

The optional ?limit= is bounded so crawlers and the Atlas page can use one stable, small response. It is cache-busted by every normal Atlas publish/edit path through invalidate_topic_caches.