feat(store): order video list by published_at, NULLS LAST

ListVideos now sorts summarized-first, then published_at DESC with undated
videos last, then seen_at DESC as a tiebreak (was seen_at only). Aligns the
list with the recency framing — newest content surfaces first — so the
recency-bounded feed reads coherently (UX review B2).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

internal/adapters/store/reads.go

@@ -141,8 +141,11 @@ const selectVideo = `
 	  FROM videos v
 	  LEFT JOIN summaries s ON s.video_id = v.id AND s.user_id = v.user_id`
 
-// ListVideos returns ALL of the user's videos — summarized first then most recent
-// by seen_at — capped at limit (non-positive defaults to 500). Unsummarized
+// ListVideos returns ALL of the user's videos — summarized first, then by
+// published_at DESC with undated videos last, then seen_at DESC as a tiebreak —
+// capped at limit (non-positive defaults to 500). The published_at ordering
+// aligns the list with the recency framing (newest content first); seen_at
+// breaks ties and orders same/!undated rows deterministically. Unsummarized
 // videos come back with Summarized=false and empty summary fields, so the list
 // view can render them with a "Summarize" affordance. Scoped by user_id.
 func (s *Store) ListVideos(ctx context.Context, userID string, limit int) ([]SummaryRow, error) {
@@ -154,7 +157,7 @@ func (s *Store) ListVideos(ctx context.Context, userID string, limit int) ([]Sum
 		rows, err := tx.Query(ctx,
 			selectVideo+`
 			 WHERE v.user_id = $1
-			 ORDER BY (s.id IS NOT NULL) DESC, v.seen_at DESC
+			 ORDER BY (s.id IS NOT NULL) DESC, v.published_at DESC NULLS LAST, v.seen_at DESC
 			 LIMIT $2`,
 			userID, limit)
 		if err != nil {