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/lib/plexImage.contract.test.ts

@@ -47,8 +47,10 @@ it("names each backdrop cut by the width the proxy cuts it at", () => {
 
 // Every small Plex picture asks for its card-size cut through cardImage (E31 S4e, swept in S5: the
 // playlist rows, the search box and the collection picker still fetched the 400px poster for a 32px
-// picture). A bare `src={…thumb}` is allowed only where the full cut is the point or the URL is not
-// the proxy's; the SET is pinned, so a new bare one fails here.
+// picture). A plain `src={…}` is allowed only where the full cut is the point or the URL is not the
+// proxy's; the SET is pinned, so a new one fails here. Every <img>'s src counts, wherever it sits
+// among the attributes and whatever its variable is called: the first cut of this test read only a
+// leading `src={…thumb…}` and missed two of the three sites it was written for (E31 review 2).
 const plexFiles = import.meta.glob(
   [
     "../components/{Plex,plex}*.tsx",
@@ -58,7 +60,10 @@ const plexFiles = import.meta.glob(
   { query: "?raw", import: "default", eager: true },
 );
 const ALLOWED = new Set([
+  "plexCards.tsx pic.src", // cardImage's own src (srcSet/sizes beside it): the card cut
   "plexCards.tsx c.thumb", // cast photos: the person-image route, not the image proxy
+  "PlexBrowse.tsx p.photo", // the person filter chip's headshot: the person-image route
+  "plexViews.tsx d.photo", // the person page's headshot: the same
   "PlexInfo.tsx c.thumb", // the same cast photos on the detail page
   "PlexInfo.tsx detail.thumb", // the detail page's own poster: the full cut is the point
   "plexDetailUi.tsx thumb", // the show/season header poster: the same
@@ -69,7 +74,7 @@ it("leaves no small Plex picture on the full cut", () => {
   expect(Object.keys(plexFiles).length).toBeGreaterThan(5);
   const bare = new Set<string>();
   for (const [path, src] of Object.entries(plexFiles))
-    for (const m of (src as string).matchAll(/<img\s+src=\{([^}]*thumb[^}]*)\}/g))
+    for (const m of (src as string).matchAll(/<img\b[^>]*?\bsrc=\{([^}]*)\}/g))
       bare.add(`${path.split("/").pop()} ${m[1]!.trim()}`);
   expect([...bare].filter((b) => !ALLOWED.has(b))).toEqual([]);
 });