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/ui/PriorityStepper.tsx

@@ -65,11 +65,15 @@ export function PriorityStepper({
   onPriority,
   onSet,
   size = "sm",
+  hint,
 }: {
   priority: number;
   onPriority: (delta: number) => void;
   onSet: (value: number) => void;
   size?: Size;
+  /** What the number MEANS where it is used (the tooltip, and the value's accessible name). The
+   *  platform layer does not know — a channel's priority orders the feed, another's would not. */
+  hint: string;
 }) {
   const { t } = useTranslation();
   const [editing, setEditing] = useState(false);
@@ -129,16 +133,16 @@ export function PriorityStepper({
       ? `border rounded-md overflow-hidden ${editing ? "border-accent" : "border-border"}`
       : "";
   return (
-    <Tooltip hint={t("channels.row.priorityHint")}>
+    <Tooltip hint={hint}>
       <div
         role="group"
-        aria-label={t("channels.row.priorityHint")}
+        aria-label={hint}
         className={`inline-flex items-center cursor-help ${framed}`}
       >
         <PriorityStepButton
           delta={-1}
           Icon={Minus}
-          label={t("channels.row.lowerPriority")}
+          label={t("common.priority.lower")}
           sizeCls={cls}
           onHoldStart={start}
           onStop={stop}
@@ -151,8 +155,8 @@ export function PriorityStepper({
         >
           <button
             onClick={beginEdit}
-            aria-label={t("channels.row.editPriority")}
-            title={t("channels.row.editPriority")}
+            aria-label={t("common.priority.edit")}
+            title={t("common.priority.edit")}
             className={`w-full text-center font-medium tabular-nums hover:text-accent ${editing ? "invisible" : ""}`}
           >
             {priority}
@@ -169,7 +173,7 @@ export function PriorityStepper({
                 if (e.key === "Enter") commitEdit();
                 else if (e.key === "Escape") setEditing(false);
               }}
-              aria-label={t("channels.row.priorityHint")}
+              aria-label={hint}
               className="absolute inset-0 w-full h-full text-center font-medium tabular-nums text-accent bg-card outline-hidden [appearance:textfield] [&::-webkit-inner-spin-button]:appearance-none"
             />
           )}
@@ -177,7 +181,7 @@ export function PriorityStepper({
         <PriorityStepButton
           delta={1}
           Icon={Plus}
-          label={t("channels.row.raisePriority")}
+          label={t("common.priority.raise")}
           sizeCls={cls}
           onHoldStart={start}
           onStop={stop}