Expose Background Playback toggle on tvOS, default off

Surfaces the existing iOS/macOS Background Playback setting in the tvOS
Playback settings, defaulting to off so audio stops when the user leaves
the app via the TV button. Pauses playback on .background/.inactive when
the toggle is off, regardless of audio route — the user's setting wins
over AirPlay/HomePod handoff. Also auto-shows the tvOS player controls
when returning to foreground so the paused state is immediately visible
and actionable.

Yattee/Views/Player/tvOS/TVPlayerView.swift

@@ -31,6 +31,7 @@ enum TVPlayerFocusTarget: Hashable {
 struct TVPlayerView: View {
     @Environment(\.appEnvironment) private var appEnvironment
     @Environment(\.dismiss) private var dismiss
+    @Environment(\.scenePhase) private var scenePhase
 
     // MARK: - State
 
@@ -397,6 +398,13 @@ struct TVPlayerView: View {
                 showControls()
             }
         }
+        // When app returns to foreground (e.g. after auto-pause from background),
+        // surface the controls so the user can immediately resume or navigate.
+        .onChange(of: scenePhase) { oldPhase, newPhase in
+            if newPhase == .active && oldPhase != .active {
+                showControls()
+            }
+        }
     }
 
     // MARK: - Failure Overlays