fix(shared): set fixed pagination limit for initial item fetch

- Set pagination limit to 20 for initial fetch to ensure proper infinite scrolling functionality
- Added comment提醒 do not lower the limit below 20 for the initial fetch

Author: fulleni

lib/shared/widgets/selection_page/bloc/searchable_selection_bloc.dart

@@ -99,7 +99,9 @@ class SearchableSelectionBloc
         final response = await (_arguments.repository!).readAll(
           filter: finalFilter,
           sort: _arguments.sortOptions,
-          pagination: PaginationOptions(limit: _arguments.limit),
+          pagination: const PaginationOptions(
+            limit: 20,
+          ), // Do nto lower it below 20 for the initial fetch, if the list items did not reach the bottom of the screen, the infinity scrolling will not function.
         );
 
         fetchedItems = response.items;