fix(ui): the platform layer speaks platform words; boxes scale with the text

- PriorityStepper labelled itself with channels.row.* and told every caller
  it orders the Feed; Combobox said plex.loading / plex.filter.moreRefine /
  sidebar.match on the feed sidebar. The generic strings moved to common.*,
  and what a priority MEANS arrives as the stepper's `hint` prop.
  uiI18n.contract.test.ts pins components/ui/ to the platform namespaces —
  the import boundary could never see an i18n key.
- 32 px-frozen box utilities (w-[150px], max-w-[1600px], left-[18px], …)
  became spacing-scale steps (w-37.5, max-w-400, left-4.5): identical at the
  default text size, and now they grow with the Settings slider instead of
  clipping or re-wrapping their own labels. An eslint rule refuses the px
  form beside the older text-[Npx] one, pinned by pxBox.contract.test.ts;
  measured in the browser that every new step is generated at its old px.
- chipLane's import-strip regex ran past a side-effect import into the next
  statement's `from`, hiding a lane between them; it now stops at the
  import's own `;`.

frontend/src/components/playlistColumns.tsx

@@ -59,7 +59,7 @@ export function playlistColumns({
           <button
             onClick={() => onPlay(v)}
             aria-label={`${t("card.play")} — ${v.title}`}
-            className="relative w-[62px] h-[35px] rounded-sm overflow-hidden bg-surface shrink-0 group"
+            className="relative w-15.5 h-8.75 rounded-sm overflow-hidden bg-surface shrink-0 group"
           >
             {v.thumbnail_url && (
               <img src={v.thumbnail_url} alt="" className="w-full h-full object-cover" />