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/views.templ

@@ -104,7 +104,7 @@ templ flashBanner(code string) {
 // #summary-list region; a non-HTMX request renders the whole page. flash carries
 // a one-shot notification (e.g. "connected", "registered") surfaced on arrival
 // after a POST→redirect.
-templ ListPage(rows []store.SummaryRow, f Filter, stats PipelineStats, flash string, hasConnected bool) {
+templ ListPage(b listBuckets, f Filter, stats PipelineStats, flash string, hasConnected bool) {
 	@Layout("Tapir — Summaries") {
 		@flashBanner(flash)
 		@filterForm(f)
@@ -118,7 +118,7 @@ templ ListPage(rows []store.SummaryRow, f Filter, stats PipelineStats, flash str
 			</p>
 		}
 		<div id="summary-list">
-			@summaryList(rows, hasConnected)
+			@summaryList(b, hasConnected)
 		</div>
 	}
 }
@@ -163,11 +163,14 @@ templ filterForm(f Filter) {
 	</form>
 }
 
-// summaryList is the swappable list fragment: one card per video (summarized or
-// not). Cards reflow to a single column on mobile; an empty list shows a friendly
-// first-run state instead of a blank table.
-templ summaryList(rows []store.SummaryRow, hasConnected bool) {
-	if len(rows) == 0 {
+// summaryList is the swappable list fragment. It leads with readable summaries +
+// recent un-summarized cards (b.Main), then collapses the noise so it does not
+// bury the payload (UX review B3/B4): a one-line count of caption-less videos,
+// and a single disclosure holding the older un-summarized back-catalogue. Cards
+// reflow to a single column on mobile; an empty list shows a friendly first-run
+// state instead of a blank table.
+templ summaryList(b listBuckets, hasConnected bool) {
+	if b.empty() {
 		if hasConnected {
 			<div class="empty empty-connected">
 				<strong>Your account is connected</strong>
@@ -182,10 +185,23 @@ templ summaryList(rows []store.SummaryRow, hasConnected bool) {
 		}
 	} else {
 		<ul class="cards">
-			for _, r := range rows {
+			for _, r := range b.Main {
 				@VideoCard(r)
 			}
 		</ul>
+		if b.NoCaption > 0 {
+			<p class="list-note muted">{ fmt.Sprintf("%d video(s) have no captions and can't be summarized.", b.NoCaption) }</p>
+		}
+		if len(b.Older) > 0 {
+			<details class="older-videos">
+				<summary>{ fmt.Sprintf("Show %d older videos — summarize on demand", len(b.Older)) }</summary>
+				<ul class="cards">
+					for _, r := range b.Older {
+						@VideoCard(r)
+					}
+				</ul>
+			</details>
+		}
 	}
 }