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/components/coin_card.dart

@@ -1,5 +1,5 @@
 import 'package:flutter/material.dart';
-import 'package:shadcn_ui/shadcn_ui.dart';
+import '../../core/theme/app_theme.dart';
 import '../../core/theme/app_spacing.dart';
 import '../../core/theme/app_theme_extension.dart';
 
@@ -31,11 +31,12 @@ class CoinCard extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    final theme = ShadTheme.of(context);
+    final theme = Theme.of(context);
 
-    return ShadCard(
-      padding: const EdgeInsets.all(AppSpacing.md),
-      child: InkWell(
+    return Card(
+      child: Padding(
+        padding: const EdgeInsets.all(AppSpacing.md),
+        child: InkWell(
         onTap: onTap,
         child: Row(
           children: [
@@ -66,13 +67,13 @@ class CoinCard extends StatelessWidget {
                 children: [
                   Text(
                     '$code/USDT',
-                    style: theme.textTheme.large.copyWith(
+                    style: AppTextStyles.headlineMedium(context).copyWith(
                       fontWeight: FontWeight.bold,
                     ),
                   ),
                   Text(
                     name,
-                    style: theme.textTheme.muted,
+                    style: AppTextStyles.bodyMedium(context).copyWith(color: theme.colorScheme.onSurfaceVariant),
                   ),
                 ],
               ),
@@ -95,6 +96,7 @@ class CoinCard extends StatelessWidget {
           ],
         ),
       ),
+      ),
     );
   }
 }