feat(CouponDetail): 在优惠券详情页添加券码显示

@@ -19,6 +19,7 @@
                     <view class="text-4xl font-bold text-blue-500 mb-2">
                         <text class="text-2xl">{{ reward.title }}</text>
                     </view>
+                    <view class="text-sm text-gray-500 font-medium" style="letter-spacing: 1rpx;">券码: {{  reward.id  }}</view>
                     <!-- Status Badge -->
                     <!-- <view class="mt-2">
                         <text :class="getStatusClass(reward.status)">{{ getStatusText(reward.status) }}</text>