Fix macOS black video after re-parenting the shared player view

The player video surface is a single shared MPVOGLView that is re-parented
between the mini-bar container (main window) and the expanded-player sheet
(a separate sheet window). When presenting the sheet, the new container
attaches the shared view before the old mini-bar container tears down, so
the old container's viewWillMove(toSuperview: nil) was ripping the shared
view out of its new home via removeFromSuperview() — leaving it with no
window and a black surface. Symmetric, so it also blanked the mini-bar
preview after collapsing.

Only detach the shared view if it still belongs to the container
(superview === self). Also force a repaint on window reattach so a paused
frame redraws, and extend the onAppear resumeRendering to macOS.

Yattee/Views/Player/MPVVideoView.swift

@@ -143,11 +143,12 @@ struct MPVVideoView: View {
             applies: appliesAspectRatio
         ))
         .onAppear {
-            #if os(iOS)
+            #if os(iOS) || os(macOS)
             // Resume the MPV display link when the expanded video view appears.
             // MiniPlayerView pauses rendering when its video preview hides during expand;
             // PlayerService.playerSheetDidAppear is gated behind background playback, so it
-            // can't be relied on to resume.
+            // can't be relied on to resume. On macOS this also recovers the sheet re-open
+            // black screen when the shared render view reappears without a window re-parent.
             backend.resumeRendering()
             #endif
             // Start debug updates if overlay is already visible when view appears