feat: show node connection status and traffic stats in admin panel

Enable sing-box Clash/V2Ray APIs for per-user metrics, persist cumulative
traffic in SQLite, and refresh the dashboard every five seconds.

Co-authored-by: Cursor <cursoragent@cursor.com>

docs/troubleshooting.md

@@ -37,10 +37,31 @@ curl -I "http://66.hyf2.cc/$(grep ^PANEL_PATH= /opt/jiedian/.env | cut -d= -f2)/
 
 > 443 端口已被 sing-box Reality 占用，面板走 80 端口子路径。请妥善保管 `PANEL_PATH`，相当于隐藏入口。
 
+面板可查看每个节点的 **在线状态、连接数、实时速率、累计流量**（数据来自 sing-box Clash API + V2Ray 统计，仅监听 127.0.0.1）。
+
 ---
 
 ## 常见问题
 
+### 面板流量/在线状态显示「不可用」
+
+sing-box 统计 API 未就绪，按顺序检查：
+
+```bash
+systemctl is-active sing-box
+ss -tlnp | grep -E '9090|9091'    # Clash API / V2Ray gRPC
+grep CLASH_API_SECRET /opt/jiedian/.env
+python3 /opt/jiedian/scripts/render-server.py
+systemctl restart sing-box jiedian-panel
+```
+
+升级后若未重装，需重新生成 sing-box 配置并重启服务，才会启用 `experimental.clash_api` 与 `v2ray_api`。
+
+### 在线状态始终离线但客户端能连
+
+- 有流量时面板会按速率推断在线；若仍显示离线，执行 `curl -s -H "Authorization: Bearer $(grep CLASH_API_SECRET /opt/jiedian/.env | cut -d= -f2)" http://127.0.0.1:9090/connections | head` 查看连接 metadata 是否含 user 字段
+- 修改节点或升级后需重新渲染配置：`python3 /opt/jiedian/scripts/render-server.py && systemctl restart sing-box`
+
 ### 面板打不开 / 404
 
 1. **路径不对**：必须用完整路径，末尾带 `/`，例如 `http://域名/jiedian-xxxx/login`