feat(16-01): configure Tailwind CSS and shadcn/ui

- Tailwind CSS v3 with postcss and autoprefixer
- shadcn/ui components.json and cn() utility
- Path alias @/ -> ./src/ in vite.config.ts and tsconfig.app.json
- CSS custom properties for shadcn theming (light/dark)
- tailwindcss-animate and @tailwindcss/typography plugins
- App.tsx uses cn() with Tailwind classes to verify integration

packages/web/components.json

@@ -0,0 +1,16 @@
+{
+  "$schema": "https://ui.shadcn.com/schema.json",
+  "style": "default",
+  "rsc": false,
+  "tsx": true,
+  "tailwind": {
+    "config": "tailwind.config.ts",
+    "css": "src/index.css",
+    "baseColor": "neutral",
+    "cssVariables": true
+  },
+  "aliases": {
+    "components": "@/components",
+    "utils": "@/lib/utils"
+  }
+}