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。

scripts/cluster/common.sh

@@ -5,6 +5,12 @@ set -euo pipefail
 cluster_root=$(cd "$(dirname "${BASH_SOURCE[0]}")/../.." && pwd)
 cluster_env_file=${AI_GATEWAY_CLUSTER_ENV_FILE:-"$cluster_root/.env.local"}
 cluster_ssh_key=${AI_GATEWAY_CLUSTER_SSH_KEY:-"$HOME/.ssh/id_ed25519_easyai_gateway_cluster"}
+cluster_ssh_control_dir=${AI_GATEWAY_CLUSTER_SSH_CONTROL_DIR:-"/tmp/easyai-gateway-ssh-${UID:-$(id -u)}-$$"}
+
+prepare_cluster_ssh_control_dir() {
+  (umask 077 && mkdir -p -- "$cluster_ssh_control_dir")
+  chmod 0700 "$cluster_ssh_control_dir"
+}
 
 load_cluster_env() {
   [[ -f $cluster_env_file && ! -L $cluster_env_file ]] || {
@@ -91,20 +97,30 @@ load_cluster_env() {
 cluster_ssh() {
   local host=$1
   shift
+  prepare_cluster_ssh_control_dir
   ssh \
     -i "$cluster_ssh_key" \
     -o BatchMode=yes \
+    -o ConnectionAttempts=3 \
     -o ConnectTimeout=10 \
+    -o ControlMaster=auto \
+    -o ControlPersist=120 \
+    -o "ControlPath=$cluster_ssh_control_dir/%C" \
     -o ServerAliveInterval=15 \
     -o ServerAliveCountMax=3 \
     "$host" "$@"
 }
 
 cluster_scp() {
+  prepare_cluster_ssh_control_dir
   scp \
     -i "$cluster_ssh_key" \
     -o BatchMode=yes \
+    -o ConnectionAttempts=3 \
     -o ConnectTimeout=10 \
+    -o ControlMaster=auto \
+    -o ControlPersist=120 \
+    -o "ControlPath=$cluster_ssh_control_dir/%C" \
     "$@"
 }