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

test/catalog/drama_model_test.dart

@@ -46,6 +46,23 @@ void main() {
     expect(drama.episodeCount, 12);
   });
 
+  test('should_parse_landscape_cover_for_horizontal_slots', () {
+    final card = Drama.fromCardJson(const {
+      'id': 5,
+      'title': '闪婚后',
+      'cover': '/files/cover.jpg',
+      'coverLandscape': '/files/cover-wide.jpg',
+    });
+    final legacy = Drama.fromDetailJson(const {
+      'id': 6,
+      'title': '替嫁新娘',
+      'cover': '/files/cover-2.jpg',
+    });
+
+    expect(card.coverLandscape, '/files/cover-wide.jpg');
+    expect(legacy.coverLandscape, isEmpty);
+  });
+
   test('should_count_shipped_episodes_when_detail_response_is_parsed', () {
     final drama = Drama.fromDetailJson(const {
       'id': 5,