feat(ui): the six native selects become the house controls

Owner's pick from the S7 mockups (2026-09-19): a short fixed set is a SegmentedToggle — the live
search's result count, the table's rows per page, a download profile's mode (on its own row, so the
three worded choices fit a phone) and audio format — and a longer set or the user's own list is a
FilterSelect: the profile's quality (seven heights) and the download dialog's profile.

A lint rule refuses a native <select> from now on (the canonical "FE control" row). The px-frozen
size rules also caught up with a fraction: `text-[9.5px]` had slipped past the integer-only pattern
in the Glass tuner, which is rem now.

frontend/src/lib/pxBox.contract.test.ts

@@ -21,6 +21,18 @@ describe("a px-frozen box utility", () => {
     expect(await refused("export const b = `x ${1} " + px("max-w", 240) + "`;\n")).toBe(1);
   });
 
+  // A fractional size is as frozen as a whole one: `text-[9.5px]` sat in the Glass tuner past an
+  // integer-only pattern (debt burn 2026-09).
+  it("is refused with a fractional size, for a box and for a font", async () => {
+    const px = (u: string, n: number) => `${u}-[${n}px]`;
+    expect(await refused(`export const e = "${px("w", 12.5)}";\n`)).toBe(1);
+    const eslint = new ESLint({ cwd: FRONTEND });
+    const [font] = await eslint.lintText(`export const f = "${px("text", 9.5)}";\n`, {
+      filePath: "src/components/__probe.tsx",
+    });
+    expect(font?.messages.some((m) => m.message.startsWith("px-frozen font size"))).toBe(true);
+  });
+
   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);