feat(store): OnboardBurstVideoIDs — junk-avoiding burst selection (ADR-028)

Newest-first but quality-aware: excludes a video when its duration is KNOWN and
outside [minSeconds, maxSeconds], dropping Shorts and multi-hour livestream VODs
that waste a scarce caption fetch on a poor first impression. NULL/unknown
duration is kept (degrade-open) but ranked after known-good rows. 0/0 bounds
disable the filter (pure newest-first, the reversibility lever). RLS-scoped.
NewestUnsummarizedVideoIDs is left in place for callers that want pure-newest.

internal/adapters/store/videos.go

@@ -124,6 +124,53 @@ func (s *Store) NewestUnsummarizedVideoIDs(ctx context.Context, userID string, l
 	return ids, nil
 }
 
+// OnboardBurstVideoIDs returns up to limit of the user's unsummarized videos for
+// the connect-time onboarding burst (ADR-028), newest-first but quality-aware: a
+// video is excluded when its duration is KNOWN and outside [minSeconds, maxSeconds]
+// — dropping Shorts (below min) and multi-hour livestream VODs (above max) that
+// would waste a scarce caption fetch on a poor first impression. A NULL/unknown
+// duration is kept (degrade-open) but ranked AFTER known-good rows, so a freshly
+// enriched good pick wins when both exist. minSeconds<=0 / maxSeconds<=0 each
+// disable that bound (0/0 == pure newest-first, the reversibility lever).
+// RLS-scoped via withUser; limit <= 0 returns nil.
+func (s *Store) OnboardBurstVideoIDs(ctx context.Context, userID string, limit, minSeconds, maxSeconds int) ([]string, error) {
+	if limit <= 0 {
+		return nil, nil
+	}
+	var ids []string
+	if err := s.withUser(ctx, userID, func(tx pgx.Tx) error {
+		rows, err := tx.Query(ctx,
+			`SELECT v.id
+			   FROM videos v
+			  WHERE v.user_id = $1
+			    AND NOT EXISTS (
+			          SELECT 1 FROM summaries su
+			           WHERE su.user_id = v.user_id AND su.video_id = v.id)
+			    AND NOT (
+			          v.duration_s IS NOT NULL
+			          AND ( ($3 > 0 AND v.duration_s < $3)
+			             OR ($4 > 0 AND v.duration_s > $4) ))
+			  ORDER BY (v.duration_s IS NOT NULL) DESC,
+			           v.published_at DESC NULLS LAST, v.seen_at DESC
+			  LIMIT $2`, userID, limit, minSeconds, maxSeconds)
+		if err != nil {
+			return fmt.Errorf("store: onboard burst videos: %w", err)
+		}
+		defer rows.Close()
+		for rows.Next() {
+			var id string
+			if err := rows.Scan(&id); err != nil {
+				return fmt.Errorf("store: scan onboard burst video: %w", err)
+			}
+			ids = append(ids, id)
+		}
+		return rows.Err()
+	}); err != nil {
+		return nil, err
+	}
+	return ids, nil
+}
+
 // DistinctChannels returns the user's distinct, non-empty source channel titles
 // (the channels they have videos from), alphabetically — the option list for the
 // feed's channel filter. RLS-scoped via withUser.