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/auth/password.go

@@ -0,0 +1,40 @@
+package auth
+
+import (
+	"crypto/rand"
+	"crypto/subtle"
+	"encoding/base64"
+	"fmt"
+	"strings"
+
+	"golang.org/x/crypto/argon2"
+)
+
+func HashPassword(password string) (string, error) {
+	salt := make([]byte, 16)
+	if _, err := rand.Read(salt); err != nil {
+		return "", err
+	}
+
+	hash := argon2.IDKey([]byte(password), salt, 1, 64*1024, 4, 32)
+	return fmt.Sprintf("argon2id$%s$%s", base64.RawStdEncoding.EncodeToString(salt), base64.RawStdEncoding.EncodeToString(hash)), nil
+}
+
+func VerifyPassword(hashValue, password string) bool {
+	parts := strings.Split(hashValue, "$")
+	if len(parts) != 3 || parts[0] != "argon2id" {
+		return false
+	}
+
+	salt, err := base64.RawStdEncoding.DecodeString(parts[1])
+	if err != nil {
+		return false
+	}
+	expected, err := base64.RawStdEncoding.DecodeString(parts[2])
+	if err != nil {
+		return false
+	}
+
+	actual := argon2.IDKey([]byte(password), salt, 1, 64*1024, 4, 32)
+	return subtle.ConstantTimeCompare(expected, actual) == 1
+}