feat(web): pipeline stats bar, summarized-first sort, Try now button for rate-limited videos

Three UX improvements for the pending-transcript state:
1. Summarized videos sort to top (ORDER BY (s.id IS NOT NULL) DESC, seen_at DESC)
   so completed summaries are always immediately visible without filtering.
   ListVideos default limit raised from 50 to 500 to show the full backlog.
2. Pipeline stats bar above the video list: '2 summarized · 256 fetching soon · 12
   no captions' — computed from the unfiltered row set, hidden when everything is
   summarized.
3. 'Try now' button on rate-limited cards replaces the passive 'Retrying later'
   chip. POST /v/{id}/retry-now clears rate_limited_at then calls ProcessVideo
   through the shared globalFetchGate — same rate limiting as the scheduler, safe
   under concurrent use.

internal/adapters/store/reads.go

@@ -141,20 +141,20 @@ 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 and not — most recent
-// first by seen_at, capped at limit (non-positive defaults to 50). Unsummarized
+// 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
 // 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) {
 	if limit <= 0 {
-		limit = 50
+		limit = 500
 	}
 	var out []SummaryRow
 	if err := s.withUser(ctx, userID, func(tx pgx.Tx) error {
 		rows, err := tx.Query(ctx,
 			selectVideo+`
 			 WHERE v.user_id = $1
-			 ORDER BY v.seen_at DESC
+			 ORDER BY (s.id IS NOT NULL) DESC, v.seen_at DESC
 			 LIMIT $2`,
 			userID, limit)
 		if err != nil {