feat: add catalogue check by creating a small service runner

php/config.php

@@ -24,5 +24,8 @@ define('MAIL_TO', getenv('MAIL_TO') ?: 'semesterapparate@ph-freiburg.de');
 define('BASE_PATH', __DIR__);
 define('STATIC_PATH', '/static');
 
+// Signature validation API (optional Python service)
+define('SIGNATURE_API_URL', getenv('SIGNATURE_API_URL') ?: 'http://localhost:8001');
+
 // Email regex pattern
 define('EMAIL_REGEX', '/^[^@\s]+@[^@\s]+\.[^@\s]+$/');