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

apps/lib/features/settings/presentation/widgets/account_section_card.dart

@@ -8,27 +8,29 @@ class AccountSectionCard extends StatelessWidget {
     this.title,
     this.description,
     required this.child,
-    this.backgroundColor = AppColors.white,
-    this.borderColor = AppColors.borderSecondary,
+    this.backgroundColor,
+    this.borderColor,
     this.contentPadding = const EdgeInsets.all(AppSpacing.lg),
   });
 
   final String? title;
   final String? description;
   final Widget child;
-  final Color backgroundColor;
-  final Color borderColor;
+  final Color? backgroundColor;
+  final Color? borderColor;
   final EdgeInsetsGeometry contentPadding;
 
   @override
   Widget build(BuildContext context) {
+    final colorScheme = Theme.of(context).colorScheme;
+
     return Container(
       width: double.infinity,
       padding: contentPadding,
       decoration: BoxDecoration(
-        color: backgroundColor,
+        color: backgroundColor ?? colorScheme.surface,
         borderRadius: BorderRadius.circular(AppRadius.xl),
-        border: Border.all(color: borderColor),
+        border: Border.all(color: borderColor ?? colorScheme.outlineVariant),
       ),
       child: Column(
         crossAxisAlignment: CrossAxisAlignment.start,
@@ -36,10 +38,10 @@ class AccountSectionCard extends StatelessWidget {
           if (title != null) ...[
             Text(
               title!,
-              style: const TextStyle(
+              style: TextStyle(
                 fontSize: 15,
                 fontWeight: FontWeight.w700,
-                color: AppColors.slate900,
+                color: colorScheme.onSurface,
               ),
             ),
           ],
@@ -47,10 +49,10 @@ class AccountSectionCard extends StatelessWidget {
             const SizedBox(height: AppSpacing.xs),
             Text(
               description!,
-              style: const TextStyle(
+              style: TextStyle(
                 fontSize: 13,
                 fontWeight: FontWeight.w500,
-                color: AppColors.slate500,
+                color: colorScheme.onSurfaceVariant,
               ),
             ),
           ],

apps/lib/features/settings/presentation/widgets/settings_page_scaffold.dart

@@ -25,8 +25,10 @@ class SettingsPageScaffold extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
+    final colorScheme = Theme.of(context).colorScheme;
+
     return Scaffold(
-      backgroundColor: AppColors.surfaceSecondary,
+      backgroundColor: colorScheme.surfaceContainerLow,
       resizeToAvoidBottomInset: resizeOnKeyboard,
       body: SafeArea(
         maintainBottomViewPadding: maintainBottomViewPadding,