feat: use normalized checkbox values in field handlers

src/Form/Service/ParticipantParkingFieldHandler.php

@@ -66,7 +66,7 @@ class ParticipantParkingFieldHandler extends AbstractParticipantFieldHandler
         }
 
         $parkingSelected = $this->getFieldValue($submittedData, $this->getFieldName());
-        $isParkingSelected = (bool) $parkingSelected;
+        $isParkingSelected = $this->normalizeCheckboxValue($parkingSelected);
 
         // Store boolean value for backward compatibility
         $participant->parking = $isParkingSelected;