feat: 新增 EnhancedSelect 组件，为 A2UI Dropdown 添加 Combobox 模式

- 创建 enhanced-select 组件（搜索、分组、描述、键盘导航、Glassmorphism 样式）
- 扩展 DropdownComponentSchema 支持 searchable/clearable/size/label/error 等字段
- A2UIDropdown 渲染器自动检测增强特性，按需切换标准 Select 与 Combobox 模式
- 所有新字段 optional，完全向后兼容

ccw/frontend/src/packages/a2ui-runtime/core/A2UITypes.ts

@@ -62,16 +62,31 @@ export const ButtonComponentSchema = z.object({
   }),
 });
 
-/** Dropdown/Select component */
+/** Dropdown option schema (enhanced with description, icon, disabled, group) */
+export const DropdownOptionSchema = z.object({
+  label: TextContentSchema,
+  value: z.string(),
+  description: TextContentSchema.optional(),
+  icon: z.string().optional(),
+  disabled: BooleanContentSchema.optional(),
+  group: z.string().optional(),
+});
+
+/** Dropdown/Select component (enhanced with search, form integration, styling) */
 export const DropdownComponentSchema = z.object({
   Dropdown: z.object({
-    options: z.array(z.object({
-      label: TextContentSchema,
-      value: z.string(),
-    })),
+    options: z.array(DropdownOptionSchema),
     selectedValue: TextContentSchema.optional(),
     onChange: ActionSchema,
     placeholder: z.string().optional(),
+    // Enhanced features
+    searchable: z.boolean().optional(),
+    clearable: z.boolean().optional(),
+    size: z.enum(['sm', 'default', 'lg']).optional(),
+    // Form integration
+    label: TextContentSchema.optional(),
+    required: z.boolean().optional(),
+    error: TextContentSchema.optional(),
   }),
 });
 

ccw/frontend/src/packages/a2ui-runtime/renderer/components/A2UIDropdown.tsx

@@ -1,9 +1,10 @@
 // ========================================
 // A2UI Dropdown Component Renderer
 // ========================================
-// Maps A2UI Dropdown component to shadcn/ui Select
+// Renders as EnhancedSelect (Combobox) when searchable,
+// or standard shadcn/ui Select otherwise.
 
-import React, { useState, useCallback, useEffect } from 'react';
+import { useState, useCallback, useEffect, useMemo } from 'react';
 import {
   Select,
   SelectContent,
@@ -11,25 +12,31 @@ import {
   SelectTrigger,
   SelectValue,
 } from '@/components/ui/Select';
+import { EnhancedSelect } from '@/components/ui/enhanced-select';
+import type { EnhancedSelectOption } from '@/components/ui/enhanced-select';
 import type { ComponentRenderer } from '../../core/A2UIComponentRegistry';
-import { resolveTextContent } from '../A2UIRenderer';
+import { resolveTextContent, resolveLiteralOrBinding } from '../A2UIRenderer';
 import type { DropdownComponent } from '../../core/A2UITypes';
 
-interface A2UIDropdownProps {
-  component: DropdownComponent;
-  state: Record<string, unknown>;
-  onAction: (actionId: string, params: Record<string, unknown>) => void | Promise<void>;
-  resolveBinding: (binding: { path: string }) => unknown;
-}
 
 /**
  * A2UI Dropdown Component Renderer
- * Using shadcn/ui Select with options array mapping to SelectItem
+ * Auto-selects rendering mode based on schema fields:
+ * - searchable/description/icon/group → EnhancedSelect (Combobox)
+ * - basic options only → shadcn/ui Select
  */
 export const A2UIDropdown: ComponentRenderer = ({ component, state, onAction, resolveBinding }) => {
   const dropdownComp = component as DropdownComponent;
   const { Dropdown: dropdownConfig } = dropdownComp;
 
+  // Detect if enhanced features are requested
+  const hasEnhancedFeatures = dropdownConfig.searchable ||
+    dropdownConfig.clearable ||
+    dropdownConfig.label ||
+    dropdownConfig.error ||
+    dropdownConfig.size ||
+    dropdownConfig.options.some((opt: any) => opt.description || opt.icon || opt.group || opt.disabled);
+
   // Resolve initial selected value from binding
   const getInitialValue = (): string => {
     if (!dropdownConfig.selectedValue) return '';
@@ -56,13 +63,55 @@ export const A2UIDropdown: ComponentRenderer = ({ component, state, onAction, re
     });
   }, [dropdownConfig.onChange, onAction]);
 
+  // Resolve enhanced options (always computed to satisfy hooks rules)
+  const resolvedOptions: EnhancedSelectOption[] = useMemo(() =>
+    dropdownConfig.options.map((opt: any) => ({
+      label: resolveTextContent(opt.label, resolveBinding),
+      value: opt.value,
+      description: opt.description ? resolveTextContent(opt.description, resolveBinding) : undefined,
+      icon: opt.icon || undefined,
+      disabled: opt.disabled
+        ? Boolean(resolveLiteralOrBinding(opt.disabled, resolveBinding))
+        : false,
+      group: opt.group || undefined,
+    })),
+    [dropdownConfig.options, resolveBinding]
+  );
+
+  const resolvedLabel = dropdownConfig.label
+    ? resolveTextContent(dropdownConfig.label, resolveBinding)
+    : undefined;
+
+  const resolvedError = dropdownConfig.error
+    ? resolveTextContent(dropdownConfig.error, resolveBinding)
+    : undefined;
+
+  // ========== Enhanced Mode (Combobox) ==========
+  if (hasEnhancedFeatures) {
+    return (
+      <EnhancedSelect
+        options={resolvedOptions}
+        value={selectedValue}
+        onChange={handleChange}
+        placeholder={dropdownConfig.placeholder}
+        searchable={dropdownConfig.searchable || false}
+        clearable={dropdownConfig.clearable || false}
+        size={dropdownConfig.size}
+        label={resolvedLabel}
+        required={dropdownConfig.required || false}
+        error={resolvedError}
+      />
+    );
+  }
+
+  // ========== Standard Mode (Radix Select) ==========
   return (
     <Select value={selectedValue} onValueChange={handleChange}>
       <SelectTrigger className="w-full">
         <SelectValue placeholder={dropdownConfig.placeholder} />
       </SelectTrigger>
       <SelectContent>
-        {dropdownConfig.options.map((option) => {
+        {dropdownConfig.options.map((option: any) => {
           const label = resolveTextContent(option.label, resolveBinding);
           return (
             <SelectItem key={option.value} value={option.value}>