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/ui/gridColumns.ts

@@ -1,5 +1,5 @@
 // VirtualGrid's column-count policy, extracted as a pure function so the viewport contract's UPPER
-// end is unit-testable without a layout engine (the lower end, the 1024x768 floor, needs no policy —
+// end is unit-testable without a layout engine (the lower end, the 768-wide tablet floor, needs no policy —
 // the grid simply drops to the columns that fit).
 //
 // An auto-fill grid answers "more room" with more columns, never bigger ones, so it always settles