feat(design): the field family, the dropdown trigger, native controls, the no-raw-input lint rule (E28 S3c)

- ui/Input, Textarea, InnerInput + fieldClass (A4): the >= 3:1 edge, a 2px accent
  focus edge, the danger edge for invalid, md/sm/xs/heading rungs, 1rem and 44 on touch
- ui/SelectTrigger (A5): SortControl, FilterSelect, the view switcher and the date
  filter on one trigger, a pill in a toolbar, r8 in a form
- ui/NativeControls (A6): Checkbox, CheckRow, Slider, ColorInput
- every raw input swept (~100 sites); inputCls retired; local/input-primitive
- useReturnFocus: an in-place editor hands the focus back to its trigger on
  Enter/Escape (the playlist and Plex title renames, the priority number);
  the Plex playlist rename gains Escape and an accessible name
- back to top: a round 48 FAB (owner decision); DESIGN.md A2 and the log

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

@@ -0,0 +1,43 @@
+import { fileURLToPath } from "node:url";
+
+import { ESLint } from "eslint";
+import { describe, expect, it } from "vitest";
+
+// `local/input-primitive` (eslint.config.js): every text field is ui/Input, Textarea or InnerInput and
+// every checkbox / slider / colour well a NativeControls primitive (docs/DESIGN.md A4, A6; E28 S3c).
+// ~100 hand-styled boxes were swept; this pins that the rule keeping a new one out fires, and where it
+// stands down.
+const RULE = "local/input-primitive";
+const FRONTEND = fileURLToPath(new URL("../../", import.meta.url));
+
+async function hits(source: string, filePath = "src/components/__probe.tsx"): Promise<number> {
+  const eslint = new ESLint({ cwd: FRONTEND });
+  const [result] = await eslint.lintText(source, { filePath });
+  return (result?.messages ?? []).filter((m) => m.ruleId === RULE).length;
+}
+
+describe("a hand-rolled field", () => {
+  it("is refused anywhere outside the field primitives, text box or native control", async () => {
+    const text = 'export const A = () => <input className="border px-2" />;\n';
+    expect(await hits(text)).toBe(1);
+    expect(await hits(text, "src/design-lab/__probe.tsx")).toBe(1);
+    // …and in a ui/ composite: the pager's page box is an Input too.
+    expect(await hits(text, "src/components/ui/Pager.tsx")).toBe(1);
+    expect(await hits("export const B = () => <textarea />;\n")).toBe(1);
+    expect(await hits('export const C = () => <input type="checkbox" />;\n')).toBe(1);
+    expect(await hits('export const D = () => <input type="range" />;\n')).toBe(1);
+  });
+
+  it("passes in a field primitive, for a file picker, and for the primitives themselves", async () => {
+    for (const file of ["Input.tsx", "NativeControls.tsx"])
+      expect(await hits("export const E = () => <input />;\n", `src/components/ui/${file}`)).toBe(
+        0,
+      );
+    expect(await hits('export const F = () => <input type="file" hidden />;\n')).toBe(0);
+    expect(
+      await hits(
+        'import { Input } from "./ui/Input";\nexport const G = () => <Input className="w-full" />;\n',
+      ),
+    ).toBe(0);
+  });
+});