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/AboutCell.tsx

@@ -56,7 +56,7 @@ export default function AboutCell({ text, channelId }: { text: string | null; ch
       </span>
       <PopoverSurface
         popover={pop}
-        className="glass w-[480px] overflow-y-auto px-3.5 py-3 rounded-lg animate-[fadeIn_0.12s_ease]"
+        className="glass w-120 overflow-y-auto px-3.5 py-3 rounded-lg animate-[fadeIn_0.12s_ease]"
         // min(design cap, available space): keeps the 28rem cap on a tall viewport, shrinks to fit on a
         // short one (high zoom). --fit-max-h is set by the fitHeight `size` middleware once positioned.
         style={{ maxHeight: "min(28rem, var(--fit-max-h, 28rem))" }}