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/PlayerModal.dom.test.tsx

@@ -563,6 +563,19 @@ describe("PlayerModal — the side panel on a wide window", () => {
     expect(detail).toHaveBeenCalledTimes(2);
   });
 
+  // E31 review 2: the popover below 1280 px said it the same way only by a copy nobody tested.
+  it("says it in the description popover below 1280 px too", async () => {
+    wideWindow(false);
+    vi.spyOn(api, "videoDetail").mockRejectedValue(new Error("boom"));
+    const A = vid("A", 0);
+    renderModal(
+      <PlayerModal video={A} queue={[A]} startIndex={0} onClose={() => {}} onState={() => {}} />,
+    );
+    fireEvent.click(screen.getByRole("button", { name: "player.description" }));
+    expect(await screen.findByText("player.descriptionFailed")).toBeTruthy();
+    expect(screen.queryByText("player.noDescription")).toBeNull();
+  });
+
   it("keeps the details under the video below 1280 px", () => {
     wideWindow(false);
     vi.spyOn(api, "videoDetail").mockReturnValue(new Promise(() => {}));