fix(ui): review round 2 — reveal floor, failed next page, count states, row Play

- DataTable: the reveal floor holds only in the view it was made for (Channels
  never clears its follow, so every later sort mounted rows up to it)
- Feed + Plex browse: a failed next page stops the read-ahead and shows a row
  that retries, instead of re-requesting it once a round-trip
- the YouTube Load more click uses nextPageOnClick; a contract pins NEXT_PAGE
  to the read-aheads and the click sites to nextPageOnClick
- ItemCount: a failed count says so; a stale one says updating to a screen reader
- the narrow-picture Play lift applies only where a hover row is there to clear
- PlayerModal: one description ladder for the popover and the panel, both tested
- plexImage contract reads every img src, any attribute order
- Tabs comment names who persists the sub-tab

frontend/src/components/ui/DataTable.tsx

@@ -267,19 +267,28 @@ export default function DataTable<T>({
   // Adjusted DURING render against the last seq seen (the house's key-change reset), so the frame
   // that re-sorted the row already shows its new page. Seeded with the mount's seq: arriving with a
   // stale reveal must not move a page nobody asked to move.
+  const viewOf = (p: number) =>
+    `${p}:${size}:${JSON.stringify(sort)}:${JSON.stringify(filters)}:${narrowedBy}`;
   const [revealSeen, setRevealSeen] = useState(reveal?.seq);
+  // The view the reveal was made for: the floor below holds only there. A caller keeps its reveal
+  // after the focus (Channels never clears `follow`), and a floor that outlived its view mounted every
+  // row up to that channel on each later sort or search (E31 review 2).
+  const [revealView, setRevealView] = useState<string | null>(null);
   if (reveal && reveal.seq !== revealSeen) {
     setRevealSeen(reveal.seq);
     const at = sorted.findIndex((row) => rowKey(row) === reveal.key);
-    if (at >= 0 && !allRows) setPage(Math.floor(at / size));
+    const target = at >= 0 && !allRows ? Math.floor(at / size) : safePage;
+    if (target !== safePage) setPage(target);
+    setRevealView(viewOf(target));
   }
+  const view = viewOf(safePage);
   const paged = allRows ? sorted : sorted.slice(safePage * size, safePage * size + size);
   // A long page ("All", 100) mounts its first rows at once and the rest in the background — but
   // always through the revealed row, which the caller focuses as soon as this frame commits.
   const shown = useProgressiveRows(
     paged,
-    `${safePage}:${size}:${JSON.stringify(sort)}:${JSON.stringify(filters)}:${narrowedBy}`,
-    reveal ? paged.findIndex((row) => rowKey(row) === reveal.key) : -1,
+    view,
+    reveal && revealView === view ? paged.findIndex((row) => rowKey(row) === reveal.key) : -1,
   );
 
   function toggleSort(key: string) {