Give trusted apps the user's role

Anikeen ID now sends trusted apps the user's role (admin or user) in
GET v1/user, a user read by ID and user.updated, so an app like the
Console can take its admins from Anikeen ID. Enums\Role, the Socialite
user's role and Resources\User::role()/isAdmin() expose it.

src/Id/Enums/Role.php

@@ -0,0 +1,22 @@
+<?php
+
+namespace Anikeen\Id\Enums;
+
+/**
+ * A user's role on Anikeen ID. Only trusted apps see it: `role` of GET v1/user (the Socialite
+ * user), of a user read by ID and of user.updated; other apps get none.
+ */
+class Role
+{
+    /** Runs Anikeen (the Anikeen ID admin panel). */
+    const ADMIN = 'admin';
+    const USER = 'user';
+
+    /**
+     * @return list<string>
+     */
+    public static function all(): array
+    {
+        return [self::ADMIN, self::USER];
+    }
+}