feat: 字幕展示逻辑

lib/models/video/play/subtitle.dart

@@ -0,0 +1,23 @@
+enum SubtitlePreference { off, on, withoutAi }
+
+extension SubtitlePreferenceDesc on SubtitlePreference {
+  static final List<String> _descList = [
+    '默认不显示字幕',
+    '选择第一个可用字幕',
+    '跳过自动生成(ai)字幕，选择第一个可用字幕'
+  ];
+  get description => _descList[index];
+}
+
+extension SubtitlePreferenceCode on SubtitlePreference {
+  static final List<String> _codeList = ['off', 'on', 'withoutAi'];
+  get code => _codeList[index];
+
+  static SubtitlePreference? fromCode(String code) {
+    final index = _codeList.indexOf(code);
+    if (index != -1) {
+      return SubtitlePreference.values[index];
+    }
+    return null;
+  }
+}