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/models/common/up_panel_position.dart

@@ -0,0 +1,15 @@
+enum UpPanelPosition {
+  leftFixed,
+  rightFixed,
+  leftDrawer,
+  rightDrawer,
+}
+
+extension UpPanelPositionDesc on UpPanelPosition {
+  String get values => ['left_fixed', 'right_fixed', 'left_drawer', 'right_drawer'][index];
+  String get labels => ['左侧常驻','右侧常驻','左侧抽屉','右侧抽屉'][index];
+}
+
+extension UpPanelPositionCode on UpPanelPosition {
+  int get code => [0, 1, 2, 3][index];
+}