fix : fix UserOutput type and use UserRepositoryInterface in CreateUserCommand

Change UserOutput.id from int to ?int to match User::getId() return type.
Replace EntityManagerInterface with UserRepositoryInterface in CreateUserCommand.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/Module/Core/Application/DTO/UserOutput.php

@@ -10,7 +10,7 @@ use DateTimeImmutable;
 final readonly class UserOutput
 {
     public function __construct(
-        public int $id,
+        public ?int $id,
         public string $username,
         /** @var list<string> */
         public array $roles,