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/lib/pxBox.contract.test.ts

@@ -0,0 +1,26 @@
+import { fileURLToPath } from "node:url";
+
+import { ESLint } from "eslint";
+import { describe, expect, it } from "vitest";
+
+// The px-frozen BOX rule in eslint.config.js (beside the older `text-[Npx]` one). A `no-restricted-
+// syntax` selector that matches nothing looks exactly like a clean codebase, so pin that it fires.
+const FRONTEND = fileURLToPath(new URL("../../", import.meta.url));
+
+async function refused(source: string): Promise<number> {
+  const eslint = new ESLint({ cwd: FRONTEND });
+  const [result] = await eslint.lintText(source, { filePath: "src/components/__probe.tsx" });
+  return (result?.messages ?? []).filter((m) => m.message.startsWith("px-frozen box size")).length;
+}
+
+describe("a px-frozen box utility", () => {
+  it("is refused in a string and in a template literal", async () => {
+    expect(await refused('export const a = "group w-[150px] shrink-0";\n')).toBe(1);
+    expect(await refused("export const b = `x ${1} max-w-[240px]`;\n")).toBe(1);
+  });
+
+  it("leaves the spacing scale, a rem arbitrary and a grid track alone", async () => {
+    expect(await refused('export const c = "w-37.5 max-w-60 text-[0.75rem]";\n')).toBe(0);
+    expect(await refused('export const d = "grid-cols-[1fr_240px]";\n')).toBe(0);
+  });
+});