fix: CI 改用 pnpm 解决 npm 'Exit handler never called' 崩溃

GitHub runner 上 npm install/ci 反复 'Exit handler never called!' 崩溃
（72s 无输出后退出），改用 pnpm 9 + Node 22：
- pnpm/action-setup@v4 + setup-node cache pnpm
- 生成 pnpm-lock.yaml，删除 package-lock.json
- package.json 加 packageManager 字段，scripts 统一 pnpm

.github/workflows/deploy.yml

@@ -14,18 +14,22 @@ jobs:
     steps:
       - uses: actions/checkout@v4
 
+      - uses: pnpm/action-setup@v4
+        with:
+          version: 9
+
       - uses: actions/setup-node@v4
         with:
-          node-version: '20'
+          node-version: '22'
+          cache: 'pnpm'
+          cache-dependency-path: site/pnpm-lock.yaml
 
       - name: Install dependencies
-        run: npm install --no-fund --no-audit
+        run: pnpm install --no-frozen-lockfile
         working-directory: site
-        env:
-          NODE_OPTIONS: '--max-old-space-size=4096'
 
       - name: Build site
-        run: npm run build
+        run: pnpm run build
         working-directory: site
         env:
           NODE_OPTIONS: '--max-old-space-size=4096'