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

backend/internal/config/config.go

@@ -0,0 +1,78 @@
+package config
+
+import (
+	"os"
+	"path/filepath"
+	"strconv"
+)
+
+// Config 包含 Web 管理界面的运行时配置。
+// 数据目录结构:
+//   <DataDir>/
+//     config.yaml       - 全局配置
+//     db.json           - 用户/实例元数据(简化存储)
+//     pki/              - CA 与证书(PKI 基础设施)
+//       ca.crt / ca.key / dh.pem / ta.key
+//     instances/<name>/ - 每个 OpenVPN 实例的目录
+//       server.conf
+//       pki/{issued,private,csd}
+//       ccd/             - 客户端配置目录
+//       status.log       - openvpn --status 周期输出
+//       logs/            - openvpn 运行日志
+//     clients/<inst>/<user>/ - 生成的 .ovpn 文件
+//     backups/          - 备份归档
+
+type Config struct {
+	Host       string `yaml:"host"`
+	Port       int    `yaml:"port"`
+	DataDir    string `yaml:"data_dir"`
+	JWTSecret  string `yaml:"jwt_secret"`
+	AdminUser  string `yaml:"admin_user"`
+	AdminPass  string `yaml:"admin_pass"`
+	LogLevel   string `yaml:"log_level"`
+	OpenVPNBin string `yaml:"openvpn_bin"`
+	EasyrsaBin string `yaml:"easyrsa_bin"`
+}
+
+func Load(dataDir string) *Config {
+	c := &Config{
+		Host:       getenv("OVPNMGR_HOST", "0.0.0.0"),
+		Port:       getenvInt("OVPNMGR_PORT", 8089),
+		DataDir:    dataDir,
+		JWTSecret:  getenv("OVPNMGR_JWT_SECRET", "change-me-in-prod-please"),
+		AdminUser:  getenv("OVPNMGR_ADMIN_USER", "admin"),
+		AdminPass:  getenv("OVPNMGR_ADMIN_PASS", "admin123"),
+		LogLevel:   getenv("OVPNMGR_LOG_LEVEL", "info"),
+		OpenVPNBin: getenv("OVPNMGR_OPENVPN_BIN", "openvpn"),
+		EasyrsaBin: getenv("OVPNMGR_EASYRSA_BIN", "easyrsa"),
+	}
+	return c
+}
+
+func (c *Config) PKIDir() string      { return filepath.Join(c.DataDir, "pki") }
+func (c *Config) InstancesDir() string { return filepath.Join(c.DataDir, "instances") }
+func (c *Config) InstanceDir(name string) string {
+	return filepath.Join(c.InstancesDir(), name)
+}
+func (c *Config) ClientsDir() string { return filepath.Join(c.DataDir, "clients") }
+func (c *Config) BackupsDir() string { return filepath.Join(c.DataDir, "backups") }
+func (c *Config) DBFile() string     { return filepath.Join(c.DataDir, "db.json") }
+
+func getenv(k, def string) string {
+	if v := os.Getenv(k); v != "" {
+		return v
+	}
+	return def
+}
+
+func getenvInt(k string, def int) int {
+	v := os.Getenv(k)
+	if v == "" {
+		return def
+	}
+	n, err := strconv.Atoi(v)
+	if err != nil {
+		return def
+	}
+	return n
+}