SEO: refine WebApplication alternateName and commit docs

- Home WebApplication JSON-LD: add alternateName "Open-source web-based AirDrop alternative"
- Docs: add troubleshooting for missing .next production build in deployment guides
  - docs/DEPLOYMENT.md
  - docs/DEPLOYMENT.zh-CN.md

docs/DEPLOYMENT.md

@@ -289,6 +289,39 @@ PM2 is a powerful process manager for Node.js. We will use it to run both backen
 
 ## 5. Troubleshooting
 
+### 5.1 Common error: Missing production build (.next not generated)
+
+- Symptoms:
+
+  - PM2/Next.js logs show: `Error: Could not find a production build in the '.next' directory. Try building your app with 'next build'...`
+  - Access via Nginx may return `502 Bad Gateway` (frontend upstream not ready).
+
+- Cause & Solution:
+
+  - After pulling the latest code, dependencies were not installed and the frontend was not built in the `frontend` directory; `frontend/.next` is missing or incomplete; or the build was run in the wrong directory (e.g., repo root).
+
+  - Run in the frontend directory:
+    ```bash
+    cd frontend
+    pnpm install --frozen-lockfile
+    pnpm build
+    # Then restart the frontend process (name depends on your PM2 config)
+    pm2 restart <frontend-app-name>
+    ```
+
+- Verify:
+
+  ```bash
+  test -f frontend/.next/BUILD_ID && echo "build ok"
+  curl -fsSI http://127.0.0.1:3002/ | head -n1  # if frontend listens on 3002
+  ```
+
+- Notes:
+  - After every `git pull` or frontend code change, rebuild and then restart the frontend process.
+  - Ensure PM2 `cwd` points to `frontend`. Prefer building and running with the same user to avoid `.next` permission issues.
+
+### 5.2 Other common issues
+
 - **Connection Issues:** Check firewall settings, Nginx proxy configurations, `CORS_ORIGIN` settings, and ensure all PM2 processes are running.
 - **Nginx Errors:** Use `sudo nginx -t` to check syntax and review `/var/log/nginx/error.log`.
 - **PM2 Issues:** Use `pm2 logs <app_name>` to view application logs.

docs/DEPLOYMENT.zh-CN.md

@@ -288,6 +288,39 @@ PM2 是一个强大的 Node.js 进程管理器，我们将用它来运行后端
 
 ## 5. 故障排除
 
+### 5.1 常见错误：前端生产构建缺失（.next 未生成）
+
+- 现象：
+
+  - PM2/Next.js 日志出现：`Error: Could not find a production build in the '.next' directory. Try building your app with 'next build'...`
+  - 通过 Nginx 访问可能返回 `502 Bad Gateway`（前端上游未就绪）。
+
+- 原因 & 解决：
+
+  - 拉取最新代码后未在 `frontend` 目录安装依赖并构建，`frontend/.next` 不存在或不完整；或构建在了错误目录（例如仓库根）。
+
+  - 进入前端目录执行：
+    ```bash
+    cd frontend
+    pnpm install --frozen-lockfile
+    pnpm build
+    # 然后重启前端进程（名称以你的 PM2 配置为准）
+    pm2 restart <frontend-app-name>
+    ```
+
+- 验证：
+
+  ```bash
+  test -f frontend/.next/BUILD_ID && echo "build ok"
+  curl -fsSI http://127.0.0.1:3002/ | head -n1  # 若前端监听 3002
+  ```
+
+- 备注：
+  - 每次 `git pull` 或前端代码更新后，均需重新构建再重启前端进程。
+  - 确保 PM2 的 `cwd` 指向 `frontend`，构建与运行尽量使用同一用户，避免权限导致 `.next` 不可读。
+
+### 5.2 其他常见问题
+
 - **连接问题：** 检查防火墙、Nginx 代理设置、CORS_ORIGIN 配置，确保所有 PM2 进程都在运行。
 - **Nginx 错误:** `sudo nginx -t` 检查语法，查看 `/var/log/nginx/error.log`。
 - **PM2 问题:** `pm2 logs <app_name>` 查看应用日志。

frontend/app/[lang]/page.tsx

@@ -46,7 +46,11 @@ export default async function Home({
     siteUrl,
     path: `/${lang}`,
     name: "PrivyDrop",
-    alternateName: ["PrivyDrop", "PrivyDrop APP"],
+    alternateName: [
+      "PrivyDrop",
+      "PrivyDrop APP",
+      "Open-source web-based AirDrop alternative",
+    ],
     description: messages.meta.home.description,
     inLanguage: lang,
     imageUrl: absoluteUrl("/logo.png", siteUrl),