refactor: change int to string for Id

Security/Common/Domain/User.cs

@@ -8,7 +8,7 @@ public enum TwoFactorAuthenticator
 
 public class User
 {
-    public required int Id { get; set; }
+    public required string Id { get; set; }
     public required string Username { get; set; }
     public required string Email { get; set; }
     public required string PasswordHash { get; set; }