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/PlexSearchBox.tsx

@@ -140,7 +140,7 @@ export default function PlexSearchBox() {
             id={listId}
             role="listbox"
             aria-label={t("plex.suggest.aria")}
-            className={`${SURFACE.menu} absolute left-0 right-0 top-full z-20 mt-2 max-h-[70vh] overflow-y-auto animate-[popIn_0.16s_ease]`}
+            className={`${SURFACE.menu} absolute left-0 right-0 top-full z-menu mt-2 max-h-[70vh] overflow-y-auto animate-[popIn_0.16s_ease]`}
           >
             {suggestions.length === 0 && suggestQ.isFetching && (
               <div className="px-3 py-2 text-sm text-muted">{t("plex.loading")}</div>