fix: update deployment script to correct Caddyfile path and manage server backup

Co-authored-by: Copilot <copilot@github.com>

.drone.yml

@@ -20,9 +20,11 @@ steps:
       # 创建部署目录
       - mkdir -p /opt/short-link/frontend
       # 拷贝编译产物
+      - mv /opt/short-link/short-link-server /opt/short-link/short-link-server.bak
+      - rm /opt/short-link/short-link-server
       - cp backend/short-link-server /opt/short-link/short-link-server
       - cp -r frontend/dist/* /opt/short-link/frontend/
-      - cp Caddyfile ~/projects/_conf/short-link.conf
+      - cp Caddyfile /root/projects/_conf/short-link.conf
       # 进入部署目录，用 nohup 后台启动服务（先杀死旧进程，避免端口冲突）
       - cd /opt/short-link
       - pkill -f short-link-server || true