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/PlexPlaylistView.header.dom.test.tsx

@@ -5,7 +5,7 @@
 // (E9 review). The runtime sums the WHOLE list, an unknown duration counts as nothing, and a list
 // nothing sums for says no runtime at all.
 import { describe, it, expect, vi, beforeAll, afterEach } from "vitest";
-import { render, cleanup, screen } from "@testing-library/react";
+import { render, cleanup, screen, fireEvent } from "@testing-library/react";
 import { QueryClient, QueryClientProvider } from "@tanstack/react-query";
 
 vi.mock("react-i18next", async (importOriginal) => ({
@@ -71,3 +71,21 @@ describe("PlexPlaylistView · the header's meta line", () => {
     expect(await meta([movie("1")])).toBe("plex.browse.items");
   });
 });
+
+// E28 audit: Enter on an unchanged (or emptied) title wrote the same name back to Plex, and an empty
+// one armed the focus hand-back while leaving the field open. Now both close with no write, as the
+// collection rename does.
+describe("PlexPlaylistView · rename", () => {
+  it("closes without a write when the title is unchanged or empty", async () => {
+    const write = vi.spyOn(api, "plexRenamePlaylist").mockResolvedValue({} as never);
+    await meta([movie("1", 5400)]);
+    for (const value of [null, "   "]) {
+      fireEvent.click(screen.getByRole("button", { name: "plex.playlist.rename" }));
+      const field = screen.getByRole("textbox", { name: "plex.playlist.rename" });
+      if (value !== null) fireEvent.change(field, { target: { value } });
+      fireEvent.keyDown(field, { key: "Enter" });
+      await screen.findByRole("heading", { name: "Films" });
+    }
+    expect(write).not.toHaveBeenCalled();
+  });
+});