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>

rsbuild.config.ts

@@ -0,0 +1,17 @@
+import { defineConfig } from '@rsbuild/core';
+import { pluginBabel } from '@rsbuild/plugin-babel';
+import { pluginReact } from '@rsbuild/plugin-react';
+
+// Docs: https://rsbuild.rs/config/
+export default defineConfig({
+  plugins: [
+    pluginReact(),
+    pluginBabel({
+      include: /\.[jt]sx?$/,
+      exclude: [/[\\/]node_modules[\\/]/],
+      babelLoaderOptions(opts) {
+        opts.plugins?.unshift('babel-plugin-react-compiler');
+      },
+    }),
+  ],
+});