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.
On iPad, expanding the player after collapsing left the MPV display link
paused, showing only a static frame. MiniPlayerView pauses rendering when
its video preview hides during expand, and PlayerService.playerSheetDidAppear
is gated behind background playback so it can't reliably resume.
Call resumeRendering() from MPVVideoView.onAppear so the expanded view
always restarts the display link.
