add User persistence: model, migration, eloquent + fake repo

UserModel maps users table (id, email unique, password_hash,
is_admin bool default false). EloquentUserRepository implements
UserRepository: create from CreateUserDto, find by id,
findByEmail. toDomain() materializes a User entity wrapping email
in EmailAddress vo. FakeUserRepository: in-memory map keyed by
auto-incrementing id, returns defensive copies on read (per
youngstartup pattern). composer stan script now passes
--no-progress for cleaner ci output.

backend/tests/Fakes/FakeUserRepository.php

@@ -0,0 +1,66 @@
+<?php
+
+namespace Tests\Fakes;
+
+use App\Shared\ValueObject\EmailAddress;
+use App\User\CreateUserDto;
+use App\User\User;
+use App\User\UserRepository;
+
+class FakeUserRepository implements UserRepository
+{
+    /**
+     * @var User[]
+     */
+    private array $existingUsers = [];
+
+    public function create(CreateUserDto $dto): User
+    {
+        $id = $this->getNextId();
+        $user = new User(
+            id: $id,
+            email: $dto->email,
+            passwordHash: $dto->passwordHash,
+            isAdmin: $dto->isAdmin,
+        );
+        $this->existingUsers[$id] = $user;
+
+        return $user;
+    }
+
+    public function find(int $id): ?User
+    {
+        $user = $this->existingUsers[$id] ?? null;
+        if ($user === null) {
+            return null;
+        }
+
+        return new User(
+            id: $user->getId(),
+            email: $user->getEmail(),
+            passwordHash: $user->getPasswordHash(),
+            isAdmin: $user->isAdmin(),
+        );
+    }
+
+    public function findByEmail(EmailAddress $email): ?User
+    {
+        foreach ($this->existingUsers as $user) {
+            if ($user->getEmail()->equals($email)) {
+                return new User(
+                    id: $user->getId(),
+                    email: $user->getEmail(),
+                    passwordHash: $user->getPasswordHash(),
+                    isAdmin: $user->isAdmin(),
+                );
+            }
+        }
+
+        return null;
+    }
+
+    private function getNextId(): int
+    {
+        return count($this->existingUsers) + 1;
+    }
+}