fix(design): claim audit part 1 — a closing key no longer re-presses its trigger, the Switch box and name, named z-levels (E28)

- In-place editors (Playlists heading + rail rename, Plex collection + playlist rename, PriorityStepper,
  Scheduler interval): a real Enter closed the editor, returned the focus to the trigger, and the same
  keystroke's activation pressed that trigger again - re-opening the editor, or in the rail selecting
  the renamed playlist. useReturnFocus.arm(e) now cancels the key's default (type-enforced); the rail and
  Scheduler editors do the same. The earlier tests dispatched a synthetic keydown, which has no default.
- Plex playlist rename: an unchanged or empty title closes with no write, as the collection rename does.
- Switch: a 36x24 box around the track (the 24 floor), 44 on a coarse pointer; `label` is required, and
  the Plex two-way-sync switch had no name.
- z-index: numeric z-10/z-20 and a literal 40 moved onto the named layer scale; a lint rule + contract.
- The /watch file card's Download is the filled primary: the page's one action.
- Stale comments: the 1024x768 floor, the retired glass tuner.

frontend/src/components/Scheduler.dom.test.tsx

@@ -165,6 +165,16 @@ describe("Scheduler · the job interval editor", () => {
       ),
     );
   });
+
+  // E28 audit: a real Enter re-opened the editor — the keystroke's own activation landed on the trigger
+  // the focus had just returned to. The closing keys cancel their default action.
+  it("closing by a key does not press the trigger again", async () => {
+    await mount();
+    for (const key of ["Enter", "Escape"]) {
+      fireEvent.click(screen.getByRole("button", { name: /scheduler.everyMin/ }));
+      expect(fireEvent.keyDown(intervalBox()!, { key })).toBe(false);
+    }
+  });
 });
 
 describe("Scheduler · the maintenance batch editor", () => {