Add invite-only registration mode

Support configurable on, invite-only, and off registration modes, including case-insensitive invitation checks and test coverage.

tests/Unit/Enums/RegistrationModeTest.php

@@ -0,0 +1,38 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests\Unit\Enums;
+
+use App\Enums\RegistrationMode;
+use PHPUnit\Framework\Attributes\CoversClass;
+use PHPUnit\Framework\Attributes\DataProvider;
+use PHPUnit\Framework\TestCase;
+
+#[CoversClass(RegistrationMode::class)]
+class RegistrationModeTest extends TestCase
+{
+    /**
+     * @return array<string, array{mixed, RegistrationMode}>
+     */
+    public static function configValueProvider(): array
+    {
+        return [
+            'boolean true' => [true, RegistrationMode::On],
+            'on' => ['on', RegistrationMode::On],
+            'true' => ['true', RegistrationMode::On],
+            'invite' => ['invite', RegistrationMode::InviteOnly],
+            'invite-only' => ['invite-only', RegistrationMode::InviteOnly],
+            'boolean false' => [false, RegistrationMode::Off],
+            'off' => ['off', RegistrationMode::Off],
+            'false' => ['false', RegistrationMode::Off],
+            'unknown' => ['unknown', RegistrationMode::Off],
+        ];
+    }
+
+    #[DataProvider('configValueProvider')]
+    public function test_registration_mode_is_created_from_config_value(mixed $value, RegistrationMode $expected): void
+    {
+        $this->assertSame($expected, RegistrationMode::fromConfig($value));
+    }
+}