refactor: 批量替换 shadcn_ui 为 Material Design 组件

## 样式主题重点优化

### 颜色映射（注重主题一致性）
- mutedForeground → onSurfaceVariant
- border → outline
- card → surfaceContainer
- destructive → error
- 保留所有 AppColorScheme 自定义颜色

### 文本样式映射
- theme.textTheme.h1/muted/large → AppTextStyles.xxx(context)
- 统一使用项目定义的文本样式系统

### 组件替换（20个文件）
- ShadApp → MaterialApp（移除 ShadThemeData）
- ShadButton → ElevatedButton/OutlinedButton
- ShadDialog → AlertDialog
- ShadInputFormField → MaterialInput
- ShadSelect → DropdownButtonFormField
- ShadCard → Card
- showShadDialog → showDialog

### 依赖变更
- 移除：shadcn_ui: ^0.52.1
- 添加：lucide_icons_flutter: ^2.0.0

### 业务逻辑保护
✅ 所有 onPressed/onChanged/validator 回调保持不变
✅ 所有 controller/focusNode 数据绑定保持不变
✅ 所有布局结构（Column/Row/Padding）保持不变
✅ 仅替换 UI 组件层，业务逻辑完全保留

flutter_monisuo/lib/ui/pages/trade/trade_page.dart

@@ -1,5 +1,5 @@
 import 'package:flutter/material.dart';
-import 'package:shadcn_ui/shadcn_ui.dart';
+import 'package:lucide_icons_flutter/lucide_icons.dart';
 import 'package:provider/provider.dart';
 import '../../../core/theme/app_spacing.dart';
 import '../../../core/theme/app_theme_extension.dart';
@@ -125,7 +125,7 @@ class _TradePageState extends State<TradePage>
     super.build(context);
 
     return Scaffold(
-      backgroundColor: context.colors.background,
+      backgroundColor: Theme.of(context).colorScheme.surface,
       body: Consumer2<MarketProvider, AssetProvider>(
         builder: (context, market, asset, _) {
           return SafeArea(
@@ -280,25 +280,25 @@ class _TradePageState extends State<TradePage>
   }
 
   void _showResultDialog(bool success, String title, String message) {
-    showShadDialog(
+    showDialog(
       context: context,
-      builder: (ctx) => ShadDialog.alert(
+      builder: (ctx) => AlertDialog(
         title: Row(
           children: [
             NeonIcon(
               icon: success ? Icons.check_circle : Icons.error,
               color: success
                   ? ctx.appColors.up
-                  : ctx.colors.error,
+                  : Theme.of(ctx).colorScheme.error,
               size: 24,
             ),
             SizedBox(width: AppSpacing.sm),
             Text(title),
           ],
         ),
-        description: Text(message),
+        content: Text(message),
         actions: [
-          ShadButton(
+          TextButton(
             child: const Text('確定'),
             onPressed: () => Navigator.of(ctx).pop(),
           ),