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/gateway/service.go

@@ -0,0 +1,33 @@
+package gateway
+
+import (
+	"context"
+
+	"github.com/google/uuid"
+
+	"github.com/nexavpn/nexavpn/backend/internal/wireguard"
+)
+
+type Service struct {
+	repo Repository
+}
+
+func NewService(repo Repository) *Service {
+	return &Service{repo: repo}
+}
+
+func (s *Service) List(ctx context.Context) ([]Gateway, error) {
+	return s.repo.List(ctx)
+}
+
+func (s *Service) SelectActive(ctx context.Context) (Gateway, error) {
+	return s.repo.FirstActive(ctx)
+}
+
+func (s *Service) BuildSyncBundle(ctx context.Context, gatewayID string) (wireguard.GatewayBundle, error) {
+	id, err := uuid.Parse(gatewayID)
+	if err != nil {
+		return wireguard.GatewayBundle{}, err
+	}
+	return s.repo.BuildSyncBundle(ctx, id)
+}