feat(wordcloud): 贴纸持久化（决策#4）+ dispatchOrder/persistDesignMedia 辅助

src/pages/diy/index.tsx

@@ -4,6 +4,7 @@ import { useState, useEffect } from 'react'
 import './index.scss'
 import { getProductById } from '../../utils/productConfig'
 import { getDesignList, setDesignList, updateDesign, type DesignItem, type StickerItem } from '../../utils/store'
+import { persistDesignMedia } from '../../utils/api'
 import { useThemeContext } from '../../context/ThemeContext'
 import { useSafeArea } from '../../hooks/useSafeArea'
 import { useStatusBar } from '../../hooks/useStatusBar'
@@ -241,18 +242,15 @@ export default function DIYPage() {
     return base
   }
 
-  const handleComplete = () => {
+  const handleComplete = async () => {
     if (hasOverlap) {
       Taro.showToast({ title: '贴纸不能重叠', icon: 'none' })
       return
     }
     if (designId) {
-      updateDesign(designId, {
-        designData: {
-          stickers,
-          category
-        }
-      })
+      // 贴纸/底图持久化（决策#4，R4 负责）：本地图 → COS 持久 URL，保证后端 WCD 打包可下载素材
+      const data = await persistDesignMedia({ stickers, category, version: 1 })
+      updateDesign(designId, { designData: data })
     }
     setPreviewMode(false)
     Taro.navigateTo({ url: `/pages/checkout/index?designId=${designId}` })