fix(RewardDetail): 修复分享功能中图片URL未使用缩略图的问题

使用reward.thumbnail作为分享图片URL，确保分享时显示正确的缩略图

@@ -5,7 +5,7 @@
         <!-- 内容区域 -->
             <!-- Top Image -->
             <view class="w-full h-48">
-                <image :src="reward.banner" class="w-full h-full object-cover" />
+                <image :src="reward.banner" mode="aspectFill" class="w-full h-full object-cover" />
             </view>
 
             <!-- Main Content -->
@@ -259,12 +259,12 @@ const onShareAppMessage = (res) => {
     // 确保数据已加载，提供默认值
     // const title = reward.value?.title ? `${reward.value.title}` : '精彩优惠券等你来兑换';
     const shareId = reward.value?.id || couponId.value || '';
-    // const imageUrl = reward.value?.banner || '';
+    const imageUrl = reward.value?.thumbnail || '';
 
     const shareData = {
         title: '众多抵用优惠券等你健步积分来换',
         path: addShareFlag(`/pages/RewardDetail/index?id=${shareId}`),
-        // imageUrl: imageUrl
+        imageUrl: imageUrl
     };
 
     return shareData;