docs(readme): Update deployment and database mode documentation

- Clarify database mode details in both README.md and README_EN.md
- Highlight default local database mode (IndexedDB) usage
- Remove redundant recommendation for local database configuration
- Add explanation of Supabase cloud database option
- Update notes about Vercel deployment and backend API
- Modify vercel.json to set default local database environment variable

README.md

@@ -124,9 +124,13 @@ vercel --prod
 - ✅ 支持自定义域名
 - ✅ 自动部署（Git 推送后自动更新）
 
+**✨ 数据库模式**：
+- 默认自动使用**本地数据库模式**（IndexedDB），数据存储在浏览器中
+- 无需配置任何数据库，开箱即用
+- 如需使用 Supabase 云端数据库，可在环境变量中配置
+
 **⚠️ 注意事项**：
 - Vercel 主要用于前端部署，后端 API 需单独部署
-- 推荐使用本地数据库模式（`VITE_USE_LOCAL_DB=true`）
 - 部署后可在 `/admin` 页面进行运行时配置
 
 ---

README_EN.md

@@ -124,9 +124,13 @@ vercel --prod
 - ✅ Custom domain support
 - ✅ Automatic deployment (auto-update on Git push)
 
+**✨ Database Mode**:
+- Automatically uses **local database mode** (IndexedDB) by default, data stored in browser
+- No database configuration needed, ready to use out of the box
+- To use Supabase cloud database, configure environment variables
+
 **⚠️ Important Notes**:
 - Vercel is primarily for frontend deployment; backend APIs need separate deployment
-- Recommended to use local database mode (`VITE_USE_LOCAL_DB=true`)
 - After deployment, configure runtime settings at `/admin` page
 
 ---

vercel.json

@@ -3,6 +3,11 @@
   "buildCommand": "npm run build",
   "outputDirectory": "dist",
   "framework": "vite",
+  "build": {
+    "env": {
+      "VITE_USE_LOCAL_DB": "true"
+    }
+  },
   "rewrites": [
     {
       "source": "/(.*)",