style: 优化详情页封面图片的显示样式

src/app.css

@@ -1234,12 +1234,15 @@ footer section p:first-child {
 }
 
 .detail-cover {
-  height: 400px;
+  height: auto;
   border-bottom: none;
   border-radius: 0;
   margin-bottom: 30px;
 }
 
 .detail-cover img {
+  width: 100%;
+  height: auto;
+  object-fit: contain;
   border-radius: 0;
 }