3x-ui 式共享节点改造：nodes 状态机 + nodeClients 各自凭据

- 移除 VMess 协议
- VLESS/SS2022 按用户流量统计（AnyTLS 日志解析，SS 节点级）
- sing-box v2ray_api stats 支持
- 内存优化：面板 128M，agent 64M，sing-box 64M

systemd/nexusgate-agent.service

@@ -1,12 +1,12 @@
 [Unit]
 Description=NexusGate node agent
-After=network-online.target nexusgate-xray.service
+After=network-online.target nexusgate-sing-box.service
 Wants=network-online.target
 
 [Service]
 Type=simple
 EnvironmentFile=/etc/nexusgate/agent.env
-ExecStart=/usr/bin/node /opt/nexusgate-agent/agent.js
+ExecStart=/usr/bin/node --max-old-space-size=64 --optimize-for-size /opt/nexusgate-agent/agent.js
 Restart=always
 RestartSec=5
 NoNewPrivileges=true

systemd/nexusgate-sing-box.service

@@ -6,6 +6,8 @@ Wants=network-online.target
 [Service]
 Type=simple
 User=root
+Environment=GOMEMLIMIT=64MiB
+Environment=GOGC=50
 ExecStart=/usr/local/bin/nexusgate-sing-box run -c /etc/nexusgate/sing-box/config.json
 Restart=on-failure
 RestartSec=3

systemd/nexusgate-xray.service

@@ -1,15 +0,0 @@
-[Unit]
-Description=NexusGate managed Xray core
-After=network-online.target
-Wants=network-online.target
-
-[Service]
-Type=simple
-User=root
-ExecStart=/usr/local/bin/xray run -config /etc/nexusgate/xray/config.json
-Restart=on-failure
-RestartSec=3
-LimitNOFILE=1048576
-
-[Install]
-WantedBy=multi-user.target