refactor(apps): 主题系统迁移至 ColorScheme + 扩展架构并支持 Dark Mode

apps/lib/shared/widgets/toast/toast.dart

@@ -92,6 +92,7 @@ class _ToastWidgetState extends State<_ToastWidget>
   @override
   Widget build(BuildContext context) {
     final config = ToastTypeConfig.fromType(context, widget.type);
+    final colorScheme = Theme.of(context).colorScheme;
 
     return Positioned(
       top: MediaQuery.of(context).padding.top + 12,
@@ -115,7 +116,7 @@ class _ToastWidgetState extends State<_ToastWidget>
                     border: Border.all(color: config.borderColor),
                     boxShadow: [
                       BoxShadow(
-                        color: AppColors.slate900.withValues(alpha: 0.08),
+                        color: colorScheme.shadow.withValues(alpha: 0.08),
                         blurRadius: 24,
                         offset: const Offset(0, 10),
                       ),