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/mediaPicture.contract.test.ts

@@ -3,6 +3,7 @@ import { describe, expect, it } from "vitest";
 import videoCard from "./VideoCard.tsx?raw";
 
 import {
+  MEDIA_BAR,
   MEDIA_HOVER_LAYER,
   MEDIA_PICTURE_CONTAINER,
   MEDIA_RESUME_LAYER,
@@ -24,6 +25,16 @@ describe("a media picture", () => {
     ["the Play", MEDIA_HOVER_LAYER],
     ["the Continue + Restart pair", MEDIA_RESUME_LAYER],
   ])("leaves the hover row its band when narrow: %s", (_, layer) => {
-    expect(layer.split(" ")).toContain("@max-[14rem]/pic:pb-10");
+    expect(layer.split(" ")).toContain("@max-[14rem]/pic:pb-(--bar-room)");
+  });
+
+  // E31 review 2: the lift applied to every narrow picture, and the feed's row and tile views (a
+  // 10rem thumbnail, no hover row) showed their Play 1.25rem above centre over an empty band. The band
+  // is now the row's own: set only by a box that holds one.
+  it("lifts it only where a hover row is there to clear", () => {
+    expect(MEDIA_BAR.split(" ")).toContain("media-bar");
+    expect(MEDIA_PICTURE_CONTAINER.split(" ")).toContain("has-[.media-bar]:[--bar-room:2.5rem]");
+    for (const layer of [MEDIA_HOVER_LAYER, MEDIA_RESUME_LAYER])
+      expect(layer).not.toMatch(/pic:pb-\d/);
   });
 });