style(theme): 客户端切换深色视觉风格

lib/pages/discover/widgets/discover_search_field.dart

@@ -97,7 +97,7 @@ class _DiscoverSearchFieldState extends State<DiscoverSearchField> {
           color: AppColors.card,
           borderRadius: BorderRadius.circular(_searchRadius),
           border: Border.all(
-            color: _focused ? AppColors.blue : Colors.transparent,
+            color: _focused ? AppColors.blue : AppColors.transparent,
           ),
         ),
         child: Row(

lib/pages/discover/widgets/drama_grid.dart

@@ -23,8 +23,8 @@ const double _tagChipFontSize = 11;
 const double _heatFontSize = 9;
 const double _heatIconSize = 11;
 const int _maxTags = 3;
-const Color _heatBackground = Color(0x99000000);
-const Color _tagChipBackground = Color(0xFFF4F1EE);
+const Color _heatBackground = AppColors.overlayMedium;
+const Color _tagChipBackground = AppColors.raised;
 final RegExp _tagSplitter = RegExp(r'[,/、·]');
 
 /// 剧场/分类页共用的双列剧目网格。
@@ -231,11 +231,11 @@ class _DiscoverCoverImage extends StatelessWidget {
 
   Widget _placeholder() {
     return const ColoredBox(
-      color: AppColors.card,
+      color: AppColors.raised,
       child: Center(
         child: Icon(
           Icons.image_not_supported_outlined,
-          color: AppColors.muted,
+          color: AppColors.subtle,
           size: 32,
         ),
       ),

lib/pages/discover/widgets/feed_banner_carousel.dart

@@ -183,8 +183,8 @@ class _FeedBannerCarouselState extends State<FeedBannerCarousel> {
                 begin: Alignment.topCenter,
                 end: Alignment.bottomCenter,
                 colors: drama == null
-                    ? const [Color(0x00000000), Color(0x8A0B0C10)]
-                    : const [Color(0x00000000), Color(0xE6000000)],
+                    ? const [AppColors.transparent, AppColors.bannerScrimMid]
+                    : const [AppColors.transparent, AppColors.bannerScrimEnd],
               ),
             ),
           ),
@@ -232,7 +232,7 @@ class _FeedBannerCarouselState extends State<FeedBannerCarousel> {
       child: dramaId == null
           ? card
           : Material(
-              color: Colors.transparent,
+              color: AppColors.transparent,
               borderRadius: borderRadius,
               clipBehavior: Clip.antiAlias,
               child: InkWell(