mod: 侧边栏、动态重构，排行改为首页分区，平板、折叠屏、竖屏视频新适配，播放页可隐藏黑边、截图、点踩，弹幕粗细调整，默认关闭后台播放，弹窗接受返回

lib/pages/preview/view.dart

@@ -90,7 +90,8 @@ class _ImagePreviewState extends State<ImagePreview>
               ListTile(
                 onTap: () {
                   Get.back();
-                  DownloadUtils.downloadImg(_previewController.currentImgUrl);
+                  DownloadUtils.downloadImg(
+                      context, _previewController.currentImgUrl);
                 },
                 dense: true,
                 title: const Text('保存到手机', style: TextStyle(fontSize: 14)),