feat(cover): 支持横版封面并收紧底栏图标间距

- Drama 新增 coverLandscape，WatchProgress 新增 dramaCoverLandscape
- 继续观看横幅优先使用横版封面，缺省回退竖版
- 底部导航栏图标与文字间距由 5dp 收紧至 1dp

lib/core/theme/app_dimens.dart

@@ -37,7 +37,7 @@ abstract final class AppDimens {
   static const double previewSectionTitle = 14;
   static const double chipFont = 10;
   static const double navLabel = 13;
-  static const double navLabelGap = 5;
+  static const double navLabelGap = 1;
 
   static const double buttonHeight = 48;
   static const double primaryButtonHeight = 52;