docs(readme): Add online demo section for Vercel deployment

- Update README.md and README_EN.md with new online demo section
- Add direct link to Vercel preview deployment
- Highlight key benefits of the online demo
- Update .gitignore to include .vercel directory
- Improve documentation for easier user onboarding

.gitignore

@@ -95,3 +95,4 @@ jspm_packages/
 # Temporary folders
 tmp/
 temp/
+.vercel

README.md

@@ -81,6 +81,14 @@
 
 适合快速部署和体验，无需服务器，全球 CDN 加速。
 
+#### 🌐 在线演示
+
+无需部署，直接访问在线演示：**[https://xcodereviewer-preview.vercel.app](https://xcodereviewer-preview.vercel.app)**
+
+- ✅ 开箱即用，无需配置
+- ✅ 数据存储在浏览器本地
+- ✅ 支持所有核心功能
+
 #### 方式一：一键部署按钮（推荐）⭐
 
 点击下方按钮直接部署到 Vercel：

README_EN.md

@@ -81,6 +81,14 @@ In the fast-paced world of software development, ensuring code quality is crucia
 
 Perfect for quick deployment and testing without a server, with global CDN acceleration.
 
+#### 🌐 Online Demo
+
+No deployment needed, access the online demo directly: **[https://xcodereviewer-preview.vercel.app](https://xcodereviewer-preview.vercel.app)**
+
+- ✅ Ready to use out of the box, no configuration needed
+- ✅ Data stored locally in browser
+- ✅ All core features supported
+
 #### Method 1: One-Click Deploy Button (Recommended) ⭐
 
 Click the button below to deploy directly to Vercel: