ListSummaries (recent-first, user-scoped, limit) and GetSummaryByVideo
LEFT JOIN videos for title/url/published_at, null-safe when no videos
row exists. Channel mirrors provider for now — channel_title lives on
the not-yet-migrated subscriptions table (data-model.md). New file so it
does not collide with Worker F's concurrent edits to store.go.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
