extend User entity with displayname and email confirmation

Add display_name (unique) and email_confirmed_at columns plus
matching getters, DTO fields, repo methods (findByDisplayName,
update), and migration. Existing auth tests updated to construct
User with the new params.

backend/app/User/User.php

@@ -3,14 +3,17 @@
 namespace App\User;
 
 use App\Shared\ValueObject\EmailAddress;
+use DateTimeImmutable;
 
 class User
 {
     public function __construct(
         private int $id,
         private EmailAddress $email,
+        private string $displayName,
         private string $passwordHash,
         private bool $isAdmin,
+        private ?DateTimeImmutable $emailConfirmedAt,
     ) {}
 
     public function getId(): int
@@ -23,6 +26,11 @@ class User
         return $this->email;
     }
 
+    public function getDisplayName(): string
+    {
+        return $this->displayName;
+    }
+
     public function getPasswordHash(): string
     {
         return $this->passwordHash;
@@ -32,4 +40,14 @@ class User
     {
         return $this->isAdmin;
     }
+
+    public function getEmailConfirmedAt(): ?DateTimeImmutable
+    {
+        return $this->emailConfirmedAt;
+    }
+
+    public function isEmailConfirmed(): bool
+    {
+        return $this->emailConfirmedAt !== null;
+    }
 }