feat: add monitoring agent (Go) + agent report API + cloud billing UI

- Go agent: CPU/mem/disk/port collectors, HTTP report, static binary
- Cross-compile: linux/amd64 + linux/arm64 (statically linked)
- One-line install script for all Linux distros
- Backend: POST /api/v1/agent/report (no JWT) + GET /agent/latest,history (JWT)
- CloudBilling.tsx: fixed syntax errors, stats/trends/records/alerts
- K8s menu renamed to Kubernetes管理

Signed-off-by: Logan.Li

agent/deploy/aiops-agent.service

@@ -0,0 +1,15 @@
+[Unit]
+Description=AIOps Monitoring Agent
+After=network-online.target
+Wants=network-online.target
+
+[Service]
+Type=simple
+# ← 修改为你的 AIOps 后端地址
+ExecStart=/usr/local/bin/aiops-agent -server http://YOUR_AIOPS_SERVER:8080 -interval 10 -token YOUR_TOKEN
+Restart=always
+RestartSec=5
+LimitNOFILE=65536
+
+[Install]
+WantedBy=multi-user.target