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.dom.test.tsx

@@ -17,13 +17,15 @@ afterEach(() => {
   vi.useRealTimers(); // any fake-timer test resets here so it can't leak into the next
 });
 
-const raise = () => screen.getByRole("button", { name: "channels.row.raisePriority" });
-const lower = () => screen.getByRole("button", { name: "channels.row.lowerPriority" });
-const valueBtn = () => screen.getByRole("button", { name: "channels.row.editPriority" });
+const raise = () => screen.getByRole("button", { name: "common.priority.raise" });
+const lower = () => screen.getByRole("button", { name: "common.priority.lower" });
+const valueBtn = () => screen.getByRole("button", { name: "common.priority.edit" });
 
 describe("PriorityStepper", () => {
   it("shows the current priority and both step buttons", () => {
-    render(<PriorityStepper priority={12} onPriority={vi.fn()} onSet={vi.fn()} />);
+    render(
+      <PriorityStepper hint="what it orders" priority={12} onPriority={vi.fn()} onSet={vi.fn()} />,
+    );
     expect(valueBtn().textContent).toBe("12");
     expect(raise()).toBeTruthy();
     expect(lower()).toBeTruthy();
@@ -31,14 +33,23 @@ describe("PriorityStepper", () => {
 
   it("tapping ＋ / − nudges by ±1", () => {
     const onPriority = vi.fn();
-    render(<PriorityStepper priority={0} onPriority={onPriority} onSet={vi.fn()} />);
+    render(
+      <PriorityStepper
+        hint="what it orders"
+        priority={0}
+        onPriority={onPriority}
+        onSet={vi.fn()}
+      />,
+    );
     fireEvent.click(raise());
     fireEvent.click(lower());
     expect(onPriority.mock.calls).toEqual([[1], [-1]]);
   });
 
   it("clicking the value opens an inline editor seeded with the current value", () => {
-    render(<PriorityStepper priority={7} onPriority={vi.fn()} onSet={vi.fn()} />);
+    render(
+      <PriorityStepper hint="what it orders" priority={7} onPriority={vi.fn()} onSet={vi.fn()} />,
+    );
     fireEvent.click(valueBtn());
     const input = screen.getByRole("spinbutton") as HTMLInputElement;
     expect(input.value).toBe("7");
@@ -46,7 +57,9 @@ describe("PriorityStepper", () => {
 
   it("typing a new value and pressing Enter commits it via onSet (negatives allowed)", () => {
     const onSet = vi.fn();
-    render(<PriorityStepper priority={7} onPriority={vi.fn()} onSet={onSet} />);
+    render(
+      <PriorityStepper hint="what it orders" priority={7} onPriority={vi.fn()} onSet={onSet} />,
+    );
     fireEvent.click(valueBtn());
     const input = screen.getByRole("spinbutton");
     fireEvent.change(input, { target: { value: "-3" } });
@@ -56,7 +69,9 @@ describe("PriorityStepper", () => {
 
   it("Escape cancels the edit without committing", () => {
     const onSet = vi.fn();
-    render(<PriorityStepper priority={7} onPriority={vi.fn()} onSet={onSet} />);
+    render(
+      <PriorityStepper hint="what it orders" priority={7} onPriority={vi.fn()} onSet={onSet} />,
+    );
     fireEvent.click(valueBtn());
     const input = screen.getByRole("spinbutton");
     fireEvent.change(input, { target: { value: "99" } });
@@ -68,7 +83,9 @@ describe("PriorityStepper", () => {
 
   it("committing an unchanged value does not call onSet", () => {
     const onSet = vi.fn();
-    render(<PriorityStepper priority={7} onPriority={vi.fn()} onSet={onSet} />);
+    render(
+      <PriorityStepper hint="what it orders" priority={7} onPriority={vi.fn()} onSet={onSet} />,
+    );
     fireEvent.click(valueBtn());
     fireEvent.keyDown(screen.getByRole("spinbutton"), { key: "Enter" });
     expect(onSet).not.toHaveBeenCalled();
@@ -76,7 +93,15 @@ describe("PriorityStepper", () => {
 
   it("renders the same interactive contract at size=md", () => {
     const onPriority = vi.fn();
-    render(<PriorityStepper priority={3} onPriority={onPriority} onSet={vi.fn()} size="md" />);
+    render(
+      <PriorityStepper
+        hint="what it orders"
+        priority={3}
+        onPriority={onPriority}
+        onSet={vi.fn()}
+        size="md"
+      />,
+    );
     expect(valueBtn().textContent).toBe("3");
     fireEvent.click(raise());
     expect(onPriority).toHaveBeenCalledWith(1);
@@ -85,7 +110,14 @@ describe("PriorityStepper", () => {
   it("holding a step button auto-repeats (accelerating) and suppresses the trailing click", () => {
     vi.useFakeTimers();
     const onPriority = vi.fn();
-    render(<PriorityStepper priority={0} onPriority={onPriority} onSet={vi.fn()} />);
+    render(
+      <PriorityStepper
+        hint="what it orders"
+        priority={0}
+        onPriority={onPriority}
+        onSet={vi.fn()}
+      />,
+    );
 
     fireEvent.pointerDown(raise());
     vi.advanceTimersByTime(349);
@@ -109,7 +141,14 @@ describe("PriorityStepper", () => {
   it("a quick tap (released before the hold threshold) still nudges exactly once", () => {
     vi.useFakeTimers();
     const onPriority = vi.fn();
-    render(<PriorityStepper priority={0} onPriority={onPriority} onSet={vi.fn()} />);
+    render(
+      <PriorityStepper
+        hint="what it orders"
+        priority={0}
+        onPriority={onPriority}
+        onSet={vi.fn()}
+      />,
+    );
 
     fireEvent.pointerDown(lower());
     vi.advanceTimersByTime(100); // below the threshold → no auto-repeat armed
@@ -122,7 +161,12 @@ describe("PriorityStepper", () => {
     vi.useFakeTimers();
     const onPriority = vi.fn();
     const { unmount } = render(
-      <PriorityStepper priority={0} onPriority={onPriority} onSet={vi.fn()} />,
+      <PriorityStepper
+        hint="what it orders"
+        priority={0}
+        onPriority={onPriority}
+        onSet={vi.fn()}
+      />,
     );
 
     fireEvent.pointerDown(raise());