fix(headlines-search): update source item widget to use correct arguments

- Replace deprecated EntityDetailsPageArguments constructor with entityId and contentType
- Ensure compatibility with latest routes package version

Author: fulleni

lib/headlines-search/widgets/source_item_widget.dart

@@ -24,7 +24,10 @@ class SourceItemWidget extends StatelessWidget {
       onTap: () {
         context.push(
           Routes.sourceDetails,
-          extra: EntityDetailsPageArguments(entity: source),
+          extra: EntityDetailsPageArguments(
+            entityId: source.id,
+            contentType: ContentType.source,
+          ),
         );
       },
     );