Redesign tvOS player controls with centered transport cluster

- Move Close to a top-right circular icon; bottom row reorganizes into
  left (Settings/Info/Comments), center transport (Previous/PlayPause/Next),
  and right (Queue) clusters with equal side frames so transport stays
  geometrically centered.
- Introduce a circular icon-only `TVTransportButtonStyle` (primary variant
  for Play/Pause) mirroring the new Close button look.
- Always render Previous/Next so Play/Pause position is fixed; dim and
  disable when unavailable.
- Share `isTransportDisabled` on `PlayerState` and reuse it on iOS and
  tvOS; apply it (plus symbol replace transition) to the tvOS Play/Pause
  button.

Yattee/Services/Player/PlayerState.swift

@@ -422,6 +422,16 @@ final class PlayerState {
         videoAspectRatio ?? (16.0 / 9.0)
     }
 
+    /// Whether transport controls (play/pause, seek) should be blocked because
+    /// the player isn't ready yet — loading, buffering, or waiting for the
+    /// first frame / initial buffer. Shared by iOS and tvOS control overlays.
+    var isTransportDisabled: Bool {
+        playbackState == .loading
+            || playbackState == .buffering
+            || !isFirstFrameReady
+            || !isBufferReady
+    }
+
     // MARK: - Methods
 
     /// Updates the current video and stream.