修正备份镜像检测逻辑

deploy/backup-db.sh

@@ -168,10 +168,6 @@ main() {
 
   command -v docker >/dev/null 2>&1 || fail "未找到 docker。"
   docker compose version >/dev/null 2>&1 || fail "未找到 docker compose 插件。"
-  if [[ -z "$(docker compose images backend -q 2>/dev/null)" ]]; then
-    fail "backend 镜像不存在,请先完成部署:bash deploy/ubuntu-deploy.sh"
-  fi
-
   ensure_backup_tool
 
   mkdir -p "${DB_DIR}" "${CONFIG_DIR}"