fix: multi-select问题默认使用modal而非drawer，改善checkbox间距

- DialogStyleContext: multi-select推荐样式从drawer改为modal
- A2UIPopupCard: DrawerPopup增加multi-select间距处理
- A2UICheckbox: 增大水平间距、行高和label-description间距

ccw/frontend/src/contexts/DialogStyleContext.tsx

@@ -61,7 +61,7 @@ export const DEFAULT_A2UI_PREFERENCES: A2UIPreferences = {
 const STYLE_RECOMMENDATIONS: Record<string, DialogStyle> = {
   confirm: 'modal',
   select: 'modal',
-  'multi-select': 'drawer',
+  'multi-select': 'modal',
   input: 'modal',
   'multi-question': 'drawer',
   form: 'drawer',