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/shared/modern_dialog.dart

@@ -1,6 +1,6 @@
 import 'package:flutter/material.dart';
-import 'package:shadcn_ui/shadcn_ui.dart';
 import '../../core/theme/app_spacing.dart';
+import '../../core/theme/app_theme.dart';
 
 /// 現代彈窗模板 - 基於 modernization-v2.md 規範
 ///
@@ -102,13 +102,13 @@ class ModernDialog extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    final theme = ShadTheme.of(context);
+    final theme = Theme.of(context);
 
     return Dialog(
       shape: RoundedRectangleBorder(
         borderRadius: BorderRadius.circular(AppRadius.xl),
       ),
-      backgroundColor: theme.colorScheme.card,
+      backgroundColor: theme.colorScheme.surfaceContainer,
       child: Container(
         padding: const EdgeInsets.all(AppSpacing.lg),
         constraints: const BoxConstraints(maxWidth: 400),
@@ -122,7 +122,7 @@ class ModernDialog extends StatelessWidget {
             else if (title != null)
               Text(
                 title!,
-                style: theme.textTheme.h3.copyWith(
+                style: AppTextStyles.headlineSmall(context).copyWith(
                   fontWeight: FontWeight.w600,
                 ),
               ),
@@ -132,7 +132,7 @@ class ModernDialog extends StatelessWidget {
             if (description != null) ...[
               Text(
                 description!,
-                style: theme.textTheme.muted,
+                style: AppTextStyles.bodyMedium(context).copyWith(color: theme.colorScheme.onSurfaceVariant),
               ),
               const SizedBox(height: AppSpacing.md),
             ],
@@ -166,11 +166,13 @@ class ModernDialog extends StatelessWidget {
   }
 
   Widget _buildActionButton(BuildContext context, ModernDialogAction action) {
-    final theme = ShadTheme.of(context);
+    final theme = Theme.of(context);
 
     if (action.isPrimary) {
-      return ShadButton(
-        backgroundColor: action.isDestructive ? theme.colorScheme.destructive : theme.colorScheme.primary,
+      return ElevatedButton(
+        style: ElevatedButton.styleFrom(
+          backgroundColor: action.isDestructive ? theme.colorScheme.error : theme.colorScheme.primary,
+        ),
         onPressed: () {
           Navigator.of(context).pop(action.returnValue);
           action.onPressed?.call();
@@ -179,7 +181,7 @@ class ModernDialog extends StatelessWidget {
       );
     }
 
-    return ShadButton.outline(
+    return OutlinedButton(
       onPressed: () {
         Navigator.of(context).pop(action.returnValue);
         action.onPressed?.call();