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/cmd/api/main.go

@@ -0,0 +1,48 @@
+package main
+
+import (
+	"context"
+	"log"
+	"net/http"
+	"os"
+	"os/signal"
+	"syscall"
+	"time"
+
+	"github.com/nexavpn/nexavpn/backend/internal/app"
+	"github.com/nexavpn/nexavpn/backend/internal/config"
+)
+
+func main() {
+	cfg := config.Load()
+
+	application, err := app.New(cfg)
+	if err != nil {
+		log.Fatalf("failed to initialize app: %v", err)
+	}
+	defer application.Close()
+
+	server := &http.Server{
+		Addr:              cfg.HTTPAddress,
+		Handler:           application.Router,
+		ReadHeaderTimeout: 5 * time.Second,
+	}
+
+	go func() {
+		log.Printf("nexavpn backend listening on %s", cfg.HTTPAddress)
+		if err := server.ListenAndServe(); err != nil && err != http.ErrServerClosed {
+			log.Fatalf("http server failed: %v", err)
+		}
+	}()
+
+	stop := make(chan os.Signal, 1)
+	signal.Notify(stop, syscall.SIGINT, syscall.SIGTERM)
+	<-stop
+
+	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
+	defer cancel()
+
+	if err := server.Shutdown(ctx); err != nil {
+		log.Printf("server shutdown error: %v", err)
+	}
+}