Add library build for package distribution

Add a separate Vite library build (vite.lib.config.ts + `build:lib`) that
bundles src/index.ts to ESM with React/react-dom externalised and the 97
internal `@/` imports resolved at build time, plus type declarations and
copies of tokens.css / typography.css into dist. Point package.json
exports/main/types at dist and make react a peer dependency, so ADS can be
consumed as an installed package (@geljic/ads3-design-system) rather than a
file: + `@/` alias dependency.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

vite.lib.config.ts

@@ -0,0 +1,47 @@
+import { defineConfig } from 'vite'
+import react from '@vitejs/plugin-react'
+import dts from 'vite-plugin-dts'
+import { resolve } from 'node:path'
+
+// Library build for distribution as an installable package (@geljic/ads3-design-system).
+// Kept separate from vite.config.ts so the Storybook + Vitest setup there stays untouched.
+// Build with: npm run build:lib
+export default defineConfig({
+  plugins: [
+    react(),
+    dts({
+      tsconfigPath: './tsconfig.app.json',
+      // Emit `dist/index.d.ts` (+ per-file declarations) rather than nesting under dist/src.
+      entryRoot: 'src',
+      include: ['src'],
+      exclude: [
+        'src/**/*.stories.tsx',
+        'src/**/*.test.tsx',
+        'src/main.tsx',
+        'src/App.tsx',
+        'src/**/_story-helpers*',
+      ],
+    }),
+  ],
+  resolve: {
+    // Resolve ADS's 97 internal `@/...` imports at build time so they never leak to consumers.
+    alias: { '@': resolve(__dirname, 'src') },
+  },
+  build: {
+    lib: {
+      entry: resolve(__dirname, 'src/index.ts'),
+      formats: ['es'],
+      fileName: () => 'index.js',
+    },
+    rollupOptions: {
+      // React is a peer dep — externalise it (and the automatic JSX runtime) to avoid bundling a
+      // second copy. Everything else (clsx, tailwind-merge, @floating-ui) is small and bundled.
+      external: ['react', 'react-dom', 'react/jsx-runtime'],
+      output: { preserveModules: false },
+    },
+    sourcemap: true,
+    emptyOutDir: true,
+    // Library output only — don't copy public/ (favicons, logos) into the package.
+    copyPublicDir: false,
+  },
+})