Reorder tvOS player controls and add Previous button

Close button is now the rightmost action (after Queue), matching the
user-requested layout. A Previous button sits before Next and appears
whenever a queue is present, disabled until history accumulates.

Yattee/Views/Player/tvOS/TVPlayerView.swift

@@ -16,6 +16,7 @@ enum TVPlayerFocusTarget: Hashable {
     case infoButton
     case commentsButton
     case debugButton
+    case playPrevious
     case playNext
     case closeButton
     case queueButton