feat: render room assignment as radio buttons

src/Form/Service/ParticipantFieldOptionsProvider.php

@@ -88,6 +88,8 @@ class ParticipantFieldOptionsProvider extends AbstractFieldOptionsProvider
 
             return [
                 'label' => 'Zimmer',
+                'expanded' => true,
+                'multiple' => false,
                 // No placeholder when only one room available - the only option is pre-selected
                 'placeholder' => $singleChoice ? false : 'Nicht zugeordnet',
                 'choices' => $choices,