feat(content): update create headline page to use reactive dropdown

Refactored the `create_headline_page.dart` to use the new BLoC-aware `SearchableDropdownFormField` for country selection.

- Replaced the old dropdown implementation with the new generic `SearchableDropdownFormField<Country, CreateHeadlineBloc, CreateHeadlineState>`.
- Injected the `CreateHeadlineBloc` instance into the widget.
- Provided extractor functions (`itemsExtractor`, `hasMoreExtractor`, `isLoadingExtractor`) to enable the dropdown to reactively pull data from the BLoC's state.

This change ensures that the country list in the search dialog updates automatically when more items are loaded via pagination, fixing the core UI refresh bug.

Author: fulleni

lib/content_management/view/create_headline_page.dart

@@ -214,12 +214,15 @@ class _CreateHeadlineViewState extends State<_CreateHeadlineView> {
                           .add(CreateHeadlineTopicChanged(value)),
                     ),
                     const SizedBox(height: AppSpacing.lg),
-                    SearchableDropdownFormField<Country>(
+                    SearchableDropdownFormField<Country, CreateHeadlineBloc,
+                        CreateHeadlineState>(
                       labelText: l10n.countryName,
-                      items: state.countries,
+                      bloc: context.read<CreateHeadlineBloc>(),
                       initialValue: state.eventCountry,
-                      hasMore: state.countriesHasMore,
-                      isLoading: state.status == CreateHeadlineStatus.loading,
+                      itemsExtractor: (state) => state.countries,
+                      hasMoreExtractor: (state) => state.countriesHasMore,
+                      isLoadingExtractor: (state) =>
+                          state.status == CreateHeadlineStatus.loading,
                       onChanged: (value) => context
                           .read<CreateHeadlineBloc>()
                           .add(CreateHeadlineCountryChanged(value)),