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/app/User/UserModel.php

@@ -0,0 +1,38 @@
+<?php
+
+namespace App\User;
+
+use Illuminate\Database\Eloquent\Builder;
+use Illuminate\Database\Eloquent\Model;
+
+/**
+ * @property int $id
+ * @property string $email
+ * @property string $password_hash
+ * @property bool $is_admin
+ *
+ * @method static Builder<static>|UserModel newModelQuery()
+ * @method static Builder<static>|UserModel newQuery()
+ * @method static Builder<static>|UserModel query()
+ * @method static Builder<static>|UserModel whereId($value)
+ * @method static Builder<static>|UserModel whereEmail($value)
+ * @method static Builder<static>|UserModel whereIsAdmin($value)
+ *
+ * @mixin \Eloquent
+ */
+class UserModel extends Model
+{
+    protected $table = 'users';
+
+    public $timestamps = false;
+
+    protected $fillable = [
+        'email',
+        'password_hash',
+        'is_admin',
+    ];
+
+    protected $casts = [
+        'is_admin' => 'boolean',
+    ];
+}