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/components/asset_card.dart

@@ -1,8 +1,8 @@
 import 'package:flutter/material.dart';
 import 'package:shadcn_ui/shadcn_ui.dart';
 import 'package:flutter_animate/flutter_animate.dart';
-import '../../core/theme/app_color_scheme.dart';
 import '../../core/theme/app_spacing.dart';
+import '../../core/theme/app_theme_extension.dart';
 
 /// 资产卡片组件 - 用于显示资产总览
 ///
@@ -21,24 +21,6 @@ class AssetCard extends StatelessWidget {
   final Gradient? gradient;
   final VoidCallback? onTap;
 
-  /// 默认渐变色 - Neon Blue → Electric Purple
-  static LinearGradient defaultGradientBuilder(bool isDark) => LinearGradient(
-    colors: isDark
-        ? [AppColorScheme.darkPrimary, AppColorScheme.darkSecondary]
-        : [AppColorScheme.lightPrimary, AppColorScheme.lightSecondary],
-    begin: Alignment.topLeft,
-    end: Alignment.bottomRight,
-  );
-
-  /// 翡翠渐变 - 用于盈利展示（主题感知）
-  static LinearGradient getEmeraldGradient(bool isDark) => LinearGradient(
-    colors: isDark
-        ? [AppColorScheme.darkTertiary, const Color(0xFF7de8b8)]
-        : [AppColorScheme.lightTertiary, const Color(0xFF00c987)],
-    begin: Alignment.topLeft,
-    end: Alignment.bottomRight,
-  );
-
   const AssetCard({
     super.key,
     this.title = '总资产',
@@ -54,9 +36,9 @@ class AssetCard extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     final theme = ShadTheme.of(context);
-    final colorScheme = Theme.of(context).colorScheme;
-    final isDark = Theme.of(context).brightness == Brightness.dark;
-    final cardGradient = gradient ?? defaultGradientBuilder(isDark);
+    final colorScheme = context.colors;
+    final appColors = context.appColors;
+    final cardGradient = gradient ?? appColors.assetGradient;
 
     // 主题感知颜色 - 在渐变背景上使用 onPrimary
     final primaryTextColor = colorScheme.onPrimary;
@@ -197,6 +179,7 @@ class AssetCardCompact extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     final theme = ShadTheme.of(context);
+    final appColors = context.appColors;
     final isValueUp = isUp ?? true;
 
     return ShadCard(
@@ -227,13 +210,13 @@ class AssetCardCompact extends StatelessWidget {
               Container(
                 padding: const EdgeInsets.symmetric(horizontal: 10, vertical: 6),
                 decoration: BoxDecoration(
-                  color: AppColorScheme.getChangeBackgroundColor(isValueUp),
+                  color: isValueUp ? appColors.upBackground : appColors.downBackground,
                   borderRadius: BorderRadius.circular(AppRadius.sm),
                 ),
                 child: Text(
                   change!,
                   style: TextStyle(
-                    color: AppColorScheme.getChangeColor(isValueUp),
+                    color: isValueUp ? appColors.up : appColors.down,
                     fontWeight: FontWeight.w600,
                   ),
                 ),