feat(cluster): 接入深圳专用 Worker 节点

新增深圳 K3s agent 与四节点 WireGuard 全互联接入脚本，将深圳归入香港逻辑 Worker 池并用污点限制为 Worker 专用。\n\n生产验收支持宁波 0、香港逻辑池 2 的双物理节点基线，补充副本拓扑分散、容量档位、链路巡检和零副本站点校验。\n\n已通过 Go 全量测试、go vet、govulncheck、迁移安全检查、ShellCheck、发布脚本测试、前后端 lint/test/build、Compose 与 Kubernetes 渲染校验。

scripts/cluster/common.sh

@@ -28,7 +28,8 @@ load_cluster_env() {
   CLUSTER_NINGBO_HOST=${AI_GATEWAY_NINGBO_HOST:-$AI_GATEWAY_DEPLOY_HOST}
   CLUSTER_LOS_ANGELES_HOST=${AI_GATEWAY_LOS_ANGELES_HOST:-$AI_GATEWAY_DEPLOY_HOST_2}
   CLUSTER_HONGKONG_HOST=${AI_GATEWAY_HONGKONG_HOST:-$AI_GATEWAY_DEPLOY_HOST_3}
-  export CLUSTER_NINGBO_HOST CLUSTER_LOS_ANGELES_HOST CLUSTER_HONGKONG_HOST
+  CLUSTER_SHENZHEN_HOST=${AI_GATEWAY_SHENZHEN_HOST:-}
+  export CLUSTER_NINGBO_HOST CLUSTER_LOS_ANGELES_HOST CLUSTER_HONGKONG_HOST CLUSTER_SHENZHEN_HOST
 
   for host in "$CLUSTER_NINGBO_HOST" "$CLUSTER_HONGKONG_HOST" "$CLUSTER_LOS_ANGELES_HOST"; do
     [[ $host =~ ^root@[A-Za-z0-9.-]+$ ]] || {
@@ -36,6 +37,10 @@ load_cluster_env() {
       return 1
     }
   done
+  if [[ -n $CLUSTER_SHENZHEN_HOST && ! $CLUSTER_SHENZHEN_HOST =~ ^root@[A-Za-z0-9.-]+$ ]]; then
+    echo "Shenzhen Worker host must use root@host syntax" >&2
+    return 1
+  fi
   [[ $ALI_REGION =~ ^[a-z0-9-]+$ && $ALI_BUCKET =~ ^[A-Za-z0-9.-]+$ ]] || {
     echo 'invalid OSS region or bucket' >&2
     return 1