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/home/hot_coins_section.dart

@@ -1,8 +1,8 @@
 import 'package:flutter/material.dart';
 import 'package:shadcn_ui/shadcn_ui.dart';
 import '../../../core/theme/app_theme.dart';
-import '../../../core/theme/app_color_scheme.dart';
 import '../../../core/theme/app_spacing.dart';
+import '../../../core/theme/app_theme_extension.dart';
 
 /// 首页热门币种区块
 class HotCoinsSection extends StatelessWidget {
@@ -10,9 +10,6 @@ class HotCoinsSection extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    final colorScheme = Theme.of(context).colorScheme;
-    final isDark = Theme.of(context).brightness == Brightness.dark;
-
     return Column(
       children: [
         // Title row
@@ -36,9 +33,9 @@ class HotCoinsSection extends StatelessWidget {
         // Card
         Container(
           decoration: BoxDecoration(
-            color: colorScheme.surfaceContainer,
+            color: context.colors.surfaceContainer,
             border: Border.all(
-              color: colorScheme.outlineVariant,
+              color: context.colors.outlineVariant,
               width: 1,
             ),
             borderRadius: BorderRadius.circular(AppRadius.xl),
@@ -52,13 +49,11 @@ class HotCoinsSection extends StatelessWidget {
                 price: '68,432.50',
                 change: '+2.35%',
                 isUp: true,
-                colorScheme: colorScheme,
-                isDark: isDark,
               ),
               Divider(
                 height: 1,
                 thickness: 1,
-                color: colorScheme.outlineVariant.withValues(alpha: 0.15),
+                color: context.appColors.ghostBorder,
               ),
               _CoinRow(
                 symbol: 'ETH',
@@ -67,13 +62,11 @@ class HotCoinsSection extends StatelessWidget {
                 price: '3,856.20',
                 change: '+1.82%',
                 isUp: true,
-                colorScheme: colorScheme,
-                isDark: isDark,
               ),
               Divider(
                 height: 1,
                 thickness: 1,
-                color: colorScheme.outlineVariant.withValues(alpha: 0.15),
+                color: context.appColors.ghostBorder,
               ),
               _CoinRow(
                 symbol: 'SOL',
@@ -82,8 +75,6 @@ class HotCoinsSection extends StatelessWidget {
                 price: '178.65',
                 change: '-0.94%',
                 isUp: false,
-                colorScheme: colorScheme,
-                isDark: isDark,
               ),
             ],
           ),
@@ -101,8 +92,6 @@ class _CoinRow extends StatelessWidget {
     required this.price,
     required this.change,
     required this.isUp,
-    required this.colorScheme,
-    required this.isDark,
   });
 
   final String symbol;
@@ -111,14 +100,12 @@ class _CoinRow extends StatelessWidget {
   final String price;
   final String change;
   final bool isUp;
-  final ColorScheme colorScheme;
-  final bool isDark;
 
   @override
   Widget build(BuildContext context) {
     final changeColor = isUp
-        ? AppColorScheme.getUpColor(isDark)
-        : AppColorScheme.getDownColor(isDark);
+        ? context.appColors.up
+        : context.appColors.down;
 
     return Padding(
       padding: const EdgeInsets.symmetric(vertical: 14, horizontal: AppSpacing.md),
@@ -130,13 +117,13 @@ class _CoinRow extends StatelessWidget {
             children: [
               CircleAvatar(
                 radius: 18,
-                backgroundColor: colorScheme.primary.withValues(alpha: 0.1),
+                backgroundColor: context.colors.primary.withValues(alpha: 0.1),
                 child: Text(
                   symbol,
                   style: AppTextStyles.bodySmall(context).copyWith(
                     fontSize: 10,
                     fontWeight: FontWeight.w700,
-                    color: colorScheme.primary,
+                    color: context.colors.primary,
                   ),
                 ),
               ),