Scaffold design engineering playground

Next.js 16 + TypeScript + Tailwind v4 + Motion project showcasing
interface components built on semantic design tokens:

- Light/dark/system theming from one CSS variable set, with a
  pre-paint script so a saved theme never flashes
- Button, Switch and SegmentedControl with keyboard support, ARIA
  semantics and spring motion that respects reduced-motion
- Vitest + Testing Library tests, including a token-coverage test
- /tokens page documenting colour and motion tokens

Co-Authored-By: Claude Opus 5.5 <[email protected]>

vitest.config.mts

@@ -0,0 +1,12 @@
+import react from "@vitejs/plugin-react";
+import tsconfigPaths from "vite-tsconfig-paths";
+import { defineConfig } from "vitest/config";
+
+export default defineConfig({
+  plugins: [tsconfigPaths(), react()],
+  test: {
+    environment: "jsdom",
+    setupFiles: ["./vitest.setup.ts"],
+    include: ["src/**/*.test.{ts,tsx}"],
+  },
+});