fix(tv): prefer show art for episode backdrops

close #1123

lib/media/media_item.dart

@@ -465,7 +465,12 @@ sealed class MediaItem with _$MediaItem {
 
   /// Returns hero art candidates in display-preference order.
   List<String> heroArtCandidates({required double containerAspectRatio}) {
-    final preferred = containerAspectRatio < 1.39 ? [backgroundSquarePath, artPath] : [artPath, backgroundSquarePath];
+    final preferred = switch (kind) {
+      MediaKind.episode when containerAspectRatio < 1.39 => [backgroundSquarePath, grandparentArtPath, artPath],
+      MediaKind.episode => [grandparentArtPath, artPath, backgroundSquarePath],
+      _ when containerAspectRatio < 1.39 => [backgroundSquarePath, artPath],
+      _ => [artPath, backgroundSquarePath],
+    };
 
     final candidates = <String>[];
     for (final path in preferred) {

test/media/media_item_test.dart

@@ -100,6 +100,24 @@ void main() {
       expect(movie.heroArtCandidates(containerAspectRatio: 16 / 9), ['/art', '/square']);
       expect(movie.heroArt(containerAspectRatio: 16 / 9), '/art');
     });
+
+    test('episodes prefer show art before episode art for wide hero containers', () {
+      final episode = MediaItem(
+        id: 'e1',
+        backend: MediaBackend.plex,
+        kind: MediaKind.episode,
+        title: 'Episode',
+        grandparentTitle: 'Show',
+        grandparentArtPath: '/show-art',
+        artPath: '/episode-art',
+        backgroundSquarePath: '/square',
+        serverId: 's1',
+      );
+
+      expect(episode.heroArtCandidates(containerAspectRatio: 16 / 9), ['/show-art', '/episode-art', '/square']);
+      expect(episode.heroArt(containerAspectRatio: 16 / 9), '/show-art');
+      expect(episode.heroArtCandidates(containerAspectRatio: 1.0), ['/square', '/show-art', '/episode-art']);
+    });
   });
 
   group('MediaItem.isPartiallyWatched', () {