fix: 商品海报分享未携带封面图（coverImage 未转完整 URL）

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

cfc-frontend/pages/discover-detail/product-detail/product-detail.vue

@@ -109,7 +109,7 @@
       </view>
     </view>
 
-    <ContentSharePoster :show="showPoster" :title="product.name" :coverImage="product.coverImage" :qrCodeBase64="posterQrCode" typeLabel="好物推荐" :dimensionCode="posterDimension" :priceText="priceText" :summary="product.intro" ctaText="长按识别二维码 · 查看商品" :inviteText="posterInviteText" @close="showPoster = false" />
+    <ContentSharePoster :show="showPoster" :title="product.name" :coverImage="getImageUrl(product.coverImage)" :qrCodeBase64="posterQrCode" typeLabel="好物推荐" :dimensionCode="posterDimension" :priceText="priceText" :summary="product.intro" ctaText="长按识别二维码 · 查看商品" :inviteText="posterInviteText" @close="showPoster = false" />
   </view>
 </template>