feat(content_management): add data update handler for headline editing

- Implement EditHeadlineDataUpdated event handler in EditHeadlineBloc
- Update constructor to listen for EditHeadlineDataUpdated events
- Add logic to update state with new country data when received

Author: fulleni

lib/content_management/bloc/edit_headline/edit_headline_bloc.dart

@@ -31,6 +31,7 @@ class EditHeadlineBloc extends Bloc<EditHeadlineEvent, EditHeadlineState> {
     on<EditHeadlineCountryChanged>(_onCountryChanged);
     on<EditHeadlineStatusChanged>(_onStatusChanged);
     on<EditHeadlineSubmitted>(_onSubmitted);
+    on<EditHeadlineDataUpdated>(_onDataUpdated);
   }
 
   final DataRepository<Headline> _headlinesRepository;
@@ -228,4 +229,11 @@ class EditHeadlineBloc extends Bloc<EditHeadlineEvent, EditHeadlineState> {
       );
     }
   }
+
+  void _onDataUpdated(
+    EditHeadlineDataUpdated event,
+    Emitter<EditHeadlineState> emit,
+  ) {
+    emit(state.copyWith(countries: event.countries));
+  }
 }