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/Home.tsx

@@ -65,7 +65,8 @@ const PlayerModal = lazy(() => import("./PlayerModal"));
 
 // A rail tile's slot width. `cardsSmall` is the feed's own dense card (its column bottoms out at
 // 180px), so a 200px slot is the same object the feed shows — not a Home-only variant that would
-// drift from it.
+// drift from it. Px on purpose, like that column (`VirtualGrid`'s `minCol` is a layout-engine px value,
+// see ui/README): the card also takes it as its MEASURED width, which must be real pixels.
 const YT_SLOT = 200;
 
 // How many already-offered cards the reroll remembers. Matched to the server's own cap
@@ -182,7 +183,7 @@ function Rail({
         {cards.map((c, i) => (
           <div
             key={`${c.source}:${c.kind}:${c.id}`}
-            className={c.aspect === "poster" ? "w-[150px] shrink-0" : "shrink-0"}
+            className={c.aspect === "poster" ? "w-37.5 shrink-0" : "shrink-0"}
             style={c.aspect === "poster" ? undefined : { width: YT_SLOT }}
           >
             {c.video ? (