fix(player): 使用高清首帧并稳定切集占位

lib/core/data/models/drama.dart

@@ -21,6 +21,7 @@ class Episode {
     this.likeCount,
     this.commentCount,
     this.thumbnailsUrl,
+    this.posterUrl,
   });
 
   final String id;
@@ -37,12 +38,14 @@ class Episode {
   final int? likeCount;
   final int? commentCount;
   final String? thumbnailsUrl;
+  final String? posterUrl;
 
   Episode withVideoUrl(
     String url, {
     int? likeCount,
     int? commentCount,
     String? thumbnailsUrl,
+    String? posterUrl,
   }) => Episode(
     id: id,
     number: number,
@@ -54,6 +57,7 @@ class Episode {
     likeCount: likeCount ?? this.likeCount,
     commentCount: commentCount ?? this.commentCount,
     thumbnailsUrl: thumbnailsUrl ?? this.thumbnailsUrl,
+    posterUrl: posterUrl ?? this.posterUrl,
   );
 
   factory Episode.fromJson(Map<String, dynamic> json) {
@@ -68,6 +72,7 @@ class Episode {
       likeCount: _optionalInt(json['likeCount']),
       commentCount: _optionalInt(json['commentCount']),
       thumbnailsUrl: _optionalString(json['thumbnailsUrl']),
+      posterUrl: _optionalString(json['posterUrl']),
     );
   }
 }
@@ -324,4 +329,4 @@ String _genreText(List<Map<String, String>> types, Object? fallback) {
   final joined = names.join(' / ');
   if (joined.isNotEmpty) return joined;
   return fallback is String ? fallback : '';
-}
+}