feat: use vacation subject prefix

tests/directadmin_vacation_api_test.php

@@ -6,7 +6,9 @@ require_once PLUGIN_ROOT . '/exec/lib/DirectAdminVacationApi.php';
 test('directadmin vacation api builds scoped payload for one mailbox', function (): void {
     $api = new DirectAdminVacationApi('/usr/local/directadmin/directadmin');
     $payload = $api->buildSavePayload('info@example.com', [
-        'subject' => 'Urlop',
+        'subject_prefix' => 'Urlop',
+        'reply_every_message' => false,
+        'repeat_minutes' => 1440,
         'body' => 'Body',
         'start_value' => '2026-06-10|morning',
         'end_value' => '2026-06-24|evening',
@@ -15,6 +17,8 @@ test('directadmin vacation api builds scoped payload for one mailbox', function
     assert_same('info', $payload['user']);
     assert_same('example.com', $payload['domain']);
     assert_same('Body', $payload['text']);
+    assert_same('Urlop', $payload['subject_prefix']);
+    assert_same('1440', $payload['reply_frequency']);
     assert_same('morning', $payload['starttime']);
     assert_same('evening', $payload['endtime']);
 });