fix: improve event editing UX and allday toggle behavior

- Fix allday toggle: when unchecking allday, set end date = start date with rounded time (30min intervals)
- Fix ResponsiveDialog CSS: set height only for expanded mode, remove maxHeight from normal mode
- Show repeat info when editing solo instance of recurring event (checkbox checked and disabled)
- Clear old event UI when updating recurring event allday status

src/features/Events/EventUpdateModal.tsx

@@ -508,7 +508,8 @@ function EventUpdateModal({
 
         const repetitionRulesChanged =
           JSON.stringify(oldRepetition) !== JSON.stringify(newRepetition) ||
-          timezoneChanged;
+          timezoneChanged ||
+          event.allday !== allday;
 
         if (repetitionRulesChanged) {
           // Repetition rules changed - need server to recalculate instances