fix(deploy): 构建前端后复制到 backend/static/，避免部署旧版

之前 deploy.sh 只打包了 backend/ 目录，但前端构建输出在
client/build/，从未被复制到 backend/static/，导致部署的
始终是旧版前端。现在在 build 后自动复制。

deploy/deploy.sh

@@ -15,6 +15,10 @@ echo "=== Building frontend ==="
 cd "$APP/client"
 npm run build 2>&1 | tail -3
 
+echo "=== Copying build to backend/static/ ==="
+rm -rf "$APP/backend/static"
+cp -r "$APP/client/build" "$APP/backend/static"
+
 echo "=== Syncing files to NAS (excluding .venv) ==="
 cd "$APP"
 tar cz \