fix(flutter): 更多面板增加小窗播放入口

lib/pages/player/player_view_actions.dart

@@ -35,6 +35,9 @@ extension _PlayerViewActions on _PlayerPageState {
           },
           onClear: _hideChrome,
           onDownload: () => requestEpisodeDownload(context, episode.id),
+          onPip: logic.pictureInPicture.isPlatformSupported
+              ? () => unawaited(logic.enterPip(context))
+              : null,
         ),
       ),
     );

lib/pages/player/widgets/player_more_sheet.dart

@@ -35,6 +35,7 @@ class PlayerMoreActions {
     required this.onSpeedChanged,
     required this.onClear,
     required this.onDownload,
+    this.onPip,
   });
 
   /// 倍速变化。
@@ -45,6 +46,9 @@ class PlayerMoreActions {
 
   /// 离线缓存当前集。
   final VoidCallback onDownload;
+
+  /// 进入小窗播放；平台不支持时为 null。
+  final VoidCallback? onPip;
 }
 
 /// K29.6 精简版播放页更多面板。
@@ -113,6 +117,13 @@ class _PlayerMoreSheetState extends State<PlayerMoreSheet> {
                 title: l10n.clearPlayback,
                 onTap: _clear,
               ),
+              if (widget.actions.onPip != null)
+                _actionRow(
+                  key: const Key('player-more-pip'),
+                  icon: Icons.picture_in_picture_alt_rounded,
+                  title: l10n.pictureInPicture,
+                  onTap: () => _closeThen(widget.actions.onPip!),
+                ),
               _actionRow(
                 key: const Key('player-more-offline'),
                 icon: Icons.download_rounded,