feat(ui): improve scaffold background consistency

- Replace hardcoded Colors.black with theme.scaffoldBackgroundColor in gradient fade effects across multiple pages
- Adjust padding style in discover page for better icon alignment

Author: fulleni

lib/discover/view/discover_page.dart

@@ -174,8 +174,9 @@ class _SourceCategoryRowState extends State<_SourceCategoryRow> {
                   style: TextButton.styleFrom(
                     // Remove default padding to align the icon perfectly
                     // with the right edge.
-                    padding:
-                        const EdgeInsets.symmetric(vertical: AppSpacing.sm),
+                    padding: const EdgeInsets.symmetric(
+                      vertical: AppSpacing.sm,
+                    ),
                   ),
                   onPressed: () {
                     context.pushNamed(
@@ -230,8 +231,8 @@ class _SourceCategoryRowState extends State<_SourceCategoryRow> {
 
                 final colors = <Color>[
                   if (showStartFade) Colors.transparent,
-                  Colors.black,
-                  Colors.black,
+                  theme.scaffoldBackgroundColor,
+                  theme.scaffoldBackgroundColor,
                   if (_showEndFade) Colors.transparent,
                 ];
 

lib/headline-details/view/headline_details_page.dart

@@ -417,8 +417,8 @@ class _HeadlineDetailsPageState extends State<HeadlineDetailsPage> {
 
                 final colors = <Color>[
                   if (showStartFade) Colors.transparent,
-                  Colors.black,
-                  Colors.black,
+                  theme.scaffoldBackgroundColor,
+                  theme.scaffoldBackgroundColor,
                   if (showEndFade) Colors.transparent,
                 ];
 

lib/headlines-feed/widgets/saved_filters_bar.dart

@@ -257,8 +257,8 @@ class _SavedFiltersBarState extends State<SavedFiltersBar> {
             // Define the gradient colors and stops based on fade visibility.
             final colors = <Color>[
               if (showStartFade) Colors.transparent,
-              Colors.black,
-              Colors.black,
+              theme.scaffoldBackgroundColor,
+              theme.scaffoldBackgroundColor,
               if (showEndFade) Colors.transparent,
             ];
 

lib/shared/widgets/feed_decorators/content_collection_decorator_widget.dart

@@ -163,8 +163,8 @@ class _ContentCollectionViewState extends State<_ContentCollectionView> {
 
                 final colors = <Color>[
                   if (showStartFade) Colors.transparent,
-                  Colors.black,
-                  Colors.black,
+                  theme.scaffoldBackgroundColor,
+                  theme.scaffoldBackgroundColor,
                   if (showEndFade) Colors.transparent,
                 ];