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/eslint.config.js

@@ -318,6 +318,11 @@ const BOX_PX =
   "/(^|[\\s:])(min-|max-)?(w|h|size|left|right|top|bottom|inset|gap|p[xytrbl]?|m[xytrbl]?)-\\[[\\d.]+px\\]/";
 const BOX_PX_MESSAGE =
   "px-frozen box size doesn't scale with --font-scale: use the spacing scale (w-37.5, max-w-60), not w-[Npx].";
+// A stacking order outside the layer scale (DESIGN.md Tokens: `base < menu < chrome < … < tooltip` in
+// index.css). A numeric `z-10` equals a level today but doesn't follow it when the scale moves; name it.
+const Z_RAW = "/(^|[\\s:])-?z-([1-9]\\d*|\\[[^\\]]+\\])(?![\\w-])/";
+const Z_RAW_MESSAGE =
+  "z-index off the layer scale: use a named level (z-base, z-menu, z-chrome, z-panel, z-rail, z-overlay, z-popover, z-tooltip), not z-N or z-[…].";
 
 export default tseslint.config(
   { ignores: ["dist", "node_modules", "playwright-report", "test-results", "e2e/.auth"] },
@@ -431,6 +436,8 @@ export default tseslint.config(
         // 150px at the default size) — 32 of these were swept in the 2026-09 debt burn.
         { selector: `Literal[value=${BOX_PX}]`, message: BOX_PX_MESSAGE },
         { selector: `TemplateElement[value.raw=${BOX_PX}]`, message: BOX_PX_MESSAGE },
+        { selector: `Literal[value=${Z_RAW}]`, message: Z_RAW_MESSAGE },
+        { selector: `TemplateElement[value.raw=${Z_RAW}]`, message: Z_RAW_MESSAGE },
       ],
     },
   },