fix: ensure mandatory services are selected

src/Form/Service/ParticipantFieldOptionsProvider.php

@@ -153,8 +153,9 @@ class ParticipantFieldOptionsProvider extends AbstractFieldOptionsProvider
 
                 $attributes = [];
 
-                // Make readonly for mandatory services (pre-selection handled by service layer)
+                // Make readonly and checked for mandatory services (pre-selection handled by service layer)
                 if (true === $service->mandatory) {
+                    $attributes['checked'] = true;
                     $attributes['readonly'] = true;
                     $attributes['class'] = 'text-pink';
                     $attributes['data-tooltip'] = 'Diese Leistung ist nicht abwählbar';