Initial commit: OpenVPN Manager v1.0

OpenVPN Web management console with multi-instance support, client cert
issuance, traffic/connection auditing, certificate expiry reminders,
auto backup/restore.

Stack:
- Backend: Go 1.21+ (Gin + JWT)
- Frontend: Vue 3 + Element Plus + ECharts + Vite
- Storage: JSON file (db.json) + filesystem (pki/, instances/, clients/, backups/)

Features:
- Multi-instance OpenVPN management (independent port/proto/subnet/PKI)
- One-click client certificate issuance with .ovpn (embedded certs)
- Certificate expiry reminders (30-day threshold)
- Connection log parsing (status-version 3)
- Auto backup/restore (tar.gz)
- Audit log for all write operations
- JWT auth (12h TTL)
- One-line install.sh for Ubuntu/Debian/RHEL/Fedora

systemd/openvpn-manager.service

@@ -0,0 +1,23 @@
+[Unit]
+Description=OpenVPN Manager Web Service
+After=network-online.target
+Wants=network-online.target
+
+[Service]
+Type=simple
+User=root
+Environment=OVPNMGR_HOST=0.0.0.0
+Environment=OVPNMGR_PORT=8089
+Environment=OVPNMGR_ADMIN_USER=admin
+# 修改为你自己的初始密码(首次登录后请立刻在系统中修改)
+Environment=OVPNMGR_ADMIN_PASS=admin123
+# JWT 签名密钥,生产环境务必改成随机字符串
+Environment=OVPNMGR_JWT_SECRET=change-me-in-prod-please
+WorkingDirectory=/opt/openvpn-manager
+ExecStart=/opt/openvpn-manager/bin/openvpn-manager --data /opt/openvpn-manager/data --dist /opt/openvpn-manager/dist
+Restart=on-failure
+RestartSec=5s
+LimitNOFILE=65536
+
+[Install]
+WantedBy=multi-user.target