Convert app into @modernsk/ui component library package

- Add library entry (src/index.ts) re-exporting all components, theme,
  and TooltipProvider
- Add shippable stylesheet (src/styles/index.css): tokens + components
  only, font inlined as base64 at build time
- Build with tsup (ESM + CJS + .d.ts) and esbuild for CSS
- package.json: exports map, files, sideEffects, peerDependencies
  (react/react-dom), correct deps (radix-ui), prepare-on-install
- Fix phantom dependency: declare radix-ui, drop unused @radix-ui/themes
- Remove Storybook boilerplate, Tailwind/PostCSS (unused)
- Keep App.tsx + Rsbuild as dev-only playground (not published)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

AGENTS.md

@@ -0,0 +1,25 @@
+# AGENTS.md
+
+You are an expert in JavaScript, Rsbuild, and web application development. You write maintainable, performant, and accessible code.
+
+## Commands
+
+- `npm run dev` - Start the dev server
+- `npm run build` - Build the app for production
+- `npm run preview` - Preview the production build locally
+
+## Docs
+
+- Rsbuild: https://rsbuild.rs/llms.txt
+- Rspack: https://rspack.rs/llms.txt
+- Rslint: https://rslint.rs/llms.txt
+
+### Rslint
+
+- Run `npm run lint` to lint your code
+
+## Tools
+
+### Prettier
+
+- Run `npm run format` to format your code