Update README.md for React migration

- Update tech stack information (Vue2 → React 18)
- Add comprehensive project overview
- Include new features list
- Update development commands (yarn → npm)
- Add build instructions
- Document Node.js 20+ recommendation

🤖 Generated with [Claude Code](https://claude.ai/code)

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

readme.md

@@ -1,10 +1,45 @@
 # card
 
-- host : [card.syui.ai](https://card.syuiai)
+A React-based card collection viewer with holographic effects.
+
+## Overview
+
+- Production URL: [card.syui.ai](https://card.syui.ai)
+- API: https://api.syui.ai
+
+## Tech Stack
+
+- React 18
+- TypeScript
+- Vite
+- Tailwind CSS
+- React Query (TanStack Query)
+- React Router v6
+
+## Features
+
+- User card collections display
+- Holographic effects for special status cards
+- Favorite card highlighting
+- Responsive grid layout
+- Fast initial loading with JSON caching
+
+## Development
 
 ```sh
-$ nvm use 16
-$ yarn install
-$ yarn dev
+# Node.js 20+ recommended
+$ npm install
+$ npm run dev
 ```
 
+## Build
+
+```sh
+$ npm run build
+$ npm run preview
+```
+
+## Environment
+
+The app runs on localhost:8080 by default and uses proxy for API calls during development.
+