fix(acceptance): 复用集群 SSH 控制连接

线上验收在宁波 SSH 建连超时时于负载前失败。为集群脚本增加受限 ControlMaster 复用和仅建连阶段的 ConnectionAttempts，避免重放远程命令。\n\n生产快照导出增加三次只读重试、原子落盘和空 Pod 清理防护。已通过 bash -n、ShellCheck、production acceptance 脚本测试、人工发布脚本测试，并验证宁波真实 SSH 控制连接可复用。

tests/release/production-acceptance-script-test.sh

@@ -7,6 +7,21 @@ tmp=$(mktemp -d)
 trap 'rm -rf "$tmp"' EXIT
 
 script=$root/scripts/cluster/run-production-acceptance.sh
+
+# shellcheck source=scripts/cluster/common.sh
+source "$root/scripts/cluster/common.sh"
+ssh() {
+  printf '%s\n' "$@" >"$tmp/ssh-arguments"
+}
+cluster_ssh_key=$tmp/test-key
+cluster_ssh_control_dir=$tmp/ssh-control
+cluster_ssh root@cluster.invalid true
+grep -Fxq 'ConnectionAttempts=3' "$tmp/ssh-arguments"
+grep -Fxq 'ControlMaster=auto' "$tmp/ssh-arguments"
+grep -Fxq 'ControlPersist=120' "$tmp/ssh-arguments"
+grep -Fxq "ControlPath=$cluster_ssh_control_dir/%C" "$tmp/ssh-arguments"
+[[ $(stat -f '%Lp' "$cluster_ssh_control_dir") == 700 ]]
+
 awk '
   /^is_release_ancestor\(\)/ { capture = 1 }
   capture && /^create_and_activate_run\(\)/ { exit }