feat(web): collapse older + caption-less videos in the list

Stop the un-summarized back-catalogue from burying the readable summaries
(UX review B3/B4). One feed, with a noise-collapse — not sections:

- Summarized + recent un-summarized videos lead inline as cards.
- Un-summarized videos older than the recency window collapse into a single
  "Show N older videos — summarize on demand" disclosure (they will not
  auto-fill; they are manual-only). Window comes from App.RecencyWindow
  (= cfg.AutoSummarizeWindow); 0 disables the collapse (all inline).
- Caption-less videos collapse into one honest line ("N videos have no
  captions and can't be summarized") instead of N dead terminal cards.

bucketRows is a pure classifier (cutoff-driven; undated rows never age out);
App gains RecencyWindow + an injectable clock for the cutoff.

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

internal/web/view.go

@@ -414,6 +414,57 @@ func retryNowURL(videoID string) templ.SafeURL {
 	return templ.SafeURL("/v/" + videoID + "/retry-now")
 }
 
+// listBuckets splits the (already filtered) video list into what the list view
+// shows where, so the readable summaries are not buried under the un-summarized
+// back-catalogue (UX review B3/B4). It is one feed with a noise-collapse, not
+// separate sections:
+//   - Main: summarized videos + recent un-summarized ones — shown inline as cards.
+//   - Older: un-summarized videos published before the recency cutoff — collapsed
+//     behind a single "Show N older videos" disclosure (they will not auto-fill;
+//     they are summarize-on-demand).
+//   - NoCaption: count of un-summarized videos with no caption track — collapsed
+//     to one honest line instead of N dead terminal cards.
+type listBuckets struct {
+	Main      []store.SummaryRow
+	Older     []store.SummaryRow
+	NoCaption int
+}
+
+// bucketRows classifies rows into the list buckets given a recency cutoff. A zero
+// cutoff (recency collapse disabled) leaves Older empty — every un-summarized,
+// captioned video stays inline. Order within each bucket is preserved.
+func bucketRows(rows []store.SummaryRow, cutoff time.Time) listBuckets {
+	var b listBuckets
+	for _, r := range rows {
+		switch {
+		case r.Summarized:
+			b.Main = append(b.Main, r)
+		case r.TranscriptStatus == "none":
+			b.NoCaption++
+		case isOlder(r, cutoff):
+			b.Older = append(b.Older, r)
+		default:
+			b.Main = append(b.Main, r)
+		}
+	}
+	return b
+}
+
+// isOlder reports whether an un-summarized row falls before the recency cutoff.
+// A zero cutoff (window disabled) or an undated row is never "older" — it cannot
+// be aged out, so it stays inline rather than being hidden in the disclosure.
+func isOlder(r store.SummaryRow, cutoff time.Time) bool {
+	if cutoff.IsZero() || r.PublishedAt.IsZero() {
+		return false
+	}
+	return r.PublishedAt.Before(cutoff)
+}
+
+// empty reports whether there is nothing to show at all (drives the empty state).
+func (b listBuckets) empty() bool {
+	return len(b.Main) == 0 && len(b.Older) == 0 && b.NoCaption == 0
+}
+
 // Filter holds the list-view query parameters. Empty fields mean "no constraint".
 // Dates are kept as the raw YYYY-MM-DD strings so the form re-renders the user's
 // input verbatim; parsing happens in matchFilter.
@@ -539,6 +590,15 @@ a.btn, a.btn:visited { color: var(--accent-fg); }
 .pipeline-bar span { display: flex; align-items: center; gap: var(--s1); }
 .pipeline-bar span + span::before { content: "·"; margin-right: var(--s1); }
 .pipeline-note { margin: calc(-1 * var(--s2)) 0 var(--s3); font-size: .8rem; line-height: 1.5; max-width: 40rem; }
+/* one-line count of caption-less videos (collapsed instead of N dead cards) */
+.list-note { margin: var(--s3) 0 0; font-size: .85rem; }
+/* older un-summarized back-catalogue, collapsed behind a disclosure so it does
+   not bury the readable summaries above it */
+.older-videos { margin-top: var(--s4); }
+.older-videos > summary { cursor: pointer; font-size: .85rem; font-weight: 600; color: var(--accent); padding: var(--s2) 0; list-style: revert; }
+.older-videos > summary:hover { text-decoration: underline; }
+.older-videos[open] > summary { margin-bottom: var(--s3); }
+.older-videos .cards { margin-top: 0; }
 .card-nudge-form { display: inline; }
 .btn-quiet { font: inherit; font-size: .72rem; font-weight: 600; padding: .15rem .55rem; border-radius: 999px; border: 1px solid var(--accent); background: transparent; color: var(--accent); cursor: pointer; }
 .btn-quiet:hover { background: var(--accent-weak); }