chore: initial project scaffold with admin web, backend, desktop client, and deployment setup

Add monorepo structure for NexaVPN WireGuard control plane including:
- .gitignore for node_modules, build artifacts, and environment files
- README with project overview, monorepo layout, and quick start guide
- Admin web UI with React, Vite, TypeScript, and nginx reverse proxy
- API client with type definitions for users, devices, policies, gateways, and audit logs
- Admin pages for dashboard, users, devices, policies, g

backend/internal/config/config.go

@@ -0,0 +1,82 @@
+package config
+
+import (
+	"os"
+	"strconv"
+	"time"
+)
+
+type Config struct {
+	AppName              string
+	Environment          string
+	HTTPAddress          string
+	DatabaseURL          string
+	JWTIssuer            string
+	JWTSecret            string
+	AccessTokenTTL       time.Duration
+	RefreshTokenTTL      time.Duration
+	DefaultGatewayID     string
+	DefaultDNS           []string
+	DefaultVPNCIDR       string
+	DefaultGatewayHost   string
+	DefaultGatewayPubKey string
+}
+
+func Load() Config {
+	return Config{
+		AppName:              getenv("APP_NAME", "NexaVPN"),
+		Environment:          getenv("APP_ENV", "development"),
+		HTTPAddress:          getenv("HTTP_ADDRESS", ":8080"),
+		DatabaseURL:          getenv("DATABASE_URL", "postgres://nexavpn:nexavpn@localhost:5432/nexavpn?sslmode=disable"),
+		JWTIssuer:            getenv("JWT_ISSUER", "nexavpn"),
+		JWTSecret:            getenv("JWT_SECRET", "change-me-in-production"),
+		AccessTokenTTL:       time.Duration(getenvInt("ACCESS_TOKEN_TTL_SECONDS", 900)) * time.Second,
+		RefreshTokenTTL:      time.Duration(getenvInt("REFRESH_TOKEN_TTL_SECONDS", 2592000)) * time.Second,
+		DefaultGatewayID:     getenv("DEFAULT_GATEWAY_ID", ""),
+		DefaultDNS:           splitCSV(getenv("DEFAULT_DNS_SERVERS", "10.20.0.53")),
+		DefaultVPNCIDR:       getenv("DEFAULT_VPN_CIDR", "100.96.0.0/24"),
+		DefaultGatewayHost:   getenv("DEFAULT_GATEWAY_ENDPOINT", "vpn.example.com:51820"),
+		DefaultGatewayPubKey: getenv("DEFAULT_GATEWAY_PUBLIC_KEY", "replace-me"),
+	}
+}
+
+func getenv(key, fallback string) string {
+	if value := os.Getenv(key); value != "" {
+		return value
+	}
+
+	return fallback
+}
+
+func getenvInt(key string, fallback int) int {
+	if value := os.Getenv(key); value != "" {
+		parsed, err := strconv.Atoi(value)
+		if err == nil {
+			return parsed
+		}
+	}
+
+	return fallback
+}
+
+func splitCSV(value string) []string {
+	if value == "" {
+		return nil
+	}
+
+	var items []string
+	start := 0
+	for i := range value {
+		if value[i] == ',' {
+			if start < i {
+				items = append(items, value[start:i])
+			}
+			start = i + 1
+		}
+	}
+	if start < len(value) {
+		items = append(items, value[start:])
+	}
+
+	return items
+}