refactor(headlines-feed): remove initial capsule filter logic

Remove the use of initialSelectedCountryIsoCodes and initialSelectedSourceTypes from the SourcesFilterBloc. These values were not being used correctly, as the initial country and source type capsule selections are only ephemeral to the UI of the SourceFilterPage and are not passed via the event. Instead, they are now initialized as empty sets, meaning the filter starts with all countries and source types selected by default in the UI.

Author: fulleni

lib/headlines-feed/bloc/sources_filter_bloc.dart

@@ -42,16 +42,17 @@ class SourcesFilterBloc extends Bloc<SourcesFilterEvent, SourcesFilterState> {
           .map((s) => s.id)
           .toSet();
 
-      // Use the passed-in initial capsule selections directly
-      final initialSelectedCountryIsoCodes =
-          event.initialSelectedCountryIsoCodes;
-      final initialSelectedSourceTypes = event.initialSelectedSourceTypes;
+      // The initial country and source type capsule selections are ephemeral
+      // to the UI of the SourceFilterPage and are not passed via the event.
+      // They are initialized as empty sets here, meaning the filter starts
+      // with all countries and source types selected by default in the UI.
+      final initialSelectedCountryIsoCodes = <String>{};
+      final initialSelectedSourceTypes = <SourceType>{};
 
       final allAvailableSources = (await _sourcesRepository.readAll()).items;
 
       // Initially, display all sources. Capsules are visually set but don't filter the list yet.
       // Filtering will occur if a capsule is manually toggled.
-      // However, if initial capsule filters ARE provided, we should respect them for the initial display.
       final displayableSources = _getFilteredSources(
         allSources: allAvailableSources,
         selectedCountries: initialSelectedCountryIsoCodes,