refactor(theme): 迁移主题感知颜色至 ThemeExtension

- 创建 AppThemeColors ThemeExtension 类，统一管理主题感知颜色（涨跌色、卡片背景、渐变等）
- 从 AppColorScheme 移除主题感知辅助函数，仅保留静态颜色常量
- 在 AppTheme 中注册 ThemeExtension，支持深色/浅色主题工厂
- 重构所有 UI 组件使用 context.appColors 访问主题颜色，替代硬编码的 AppColorScheme 方法调用
- 移除组件中重复的 isDark 判断逻辑，简化颜色获取方式
- 保持向后兼容性，所有现有功能不变

flutter_monisuo/lib/ui/pages/asset/components/asset_dialogs.dart

@@ -4,6 +4,7 @@ import 'package:shadcn_ui/shadcn_ui.dart';
 import 'package:lucide_icons_flutter/lucide_icons.dart';
 import 'package:provider/provider.dart';
 import '../../../../core/theme/app_theme.dart';
+import '../../../../core/theme/app_theme_extension.dart';
 import '../../../../core/theme/app_color_scheme.dart';
 import '../../../../core/theme/app_spacing.dart';
 import '../../../../core/utils/toast_utils.dart';
@@ -246,7 +247,6 @@ void showDepositResultDialog(BuildContext context, Map<String, dynamic> data) {
   final walletAddress = data['walletAddress'] as String? ?? '';
   final walletNetwork = data['walletNetwork'] as String? ?? 'TRC20';
   final colorScheme = Theme.of(context).colorScheme;
-  final isDark = Theme.of(context).brightness == Brightness.dark;
 
   showShadDialog(
     context: context,
@@ -263,7 +263,7 @@ void showDepositResultDialog(BuildContext context, Map<String, dynamic> data) {
               children: [
                 NeonIcon(
                   icon: Icons.check_circle,
-                  color: AppColorScheme.getUpColor(isDark),
+                  color: context.appColors.up,
                   size: 24,
                 ),
                 const SizedBox(width: AppSpacing.sm),
@@ -361,7 +361,6 @@ void showWithdrawDialog(BuildContext context, String? balance) {
   final contactController = TextEditingController();
   final formKey = GlobalKey<ShadFormState>();
   final colorScheme = Theme.of(context).colorScheme;
-  final isDark = Theme.of(context).brightness == Brightness.dark;
 
   showShadDialog(
     context: context,
@@ -412,10 +411,10 @@ void showWithdrawDialog(BuildContext context, String? balance) {
                     vertical: AppSpacing.sm,
                   ),
                   decoration: BoxDecoration(
-                    color: AppColorScheme.getUpBackgroundColor(isDark),
+                    color: context.appColors.upBackground,
                     borderRadius: BorderRadius.circular(AppRadius.full),
                     border: Border.all(
-                      color: AppColorScheme.getUpColor(isDark).withValues(alpha: 0.2),
+                      color: context.appColors.up.withValues(alpha: 0.2),
                     ),
                   ),
                   child: Row(
@@ -431,7 +430,7 @@ void showWithdrawDialog(BuildContext context, String? balance) {
                         '$balance USDT',
                         style: AppTextStyles.labelLarge(context).copyWith(
                           fontWeight: FontWeight.bold,
-                          color: AppColorScheme.getUpColor(isDark),
+                          color: context.appColors.up,
                         ),
                       ),
                     ],