In sheet (inline) mode the expanded player kept a fixed size and never
reacted to the video's aspect ratio, unlike window/floating mode. Drive
the sheet's backing NSWindow size from the video aspect ratio, reusing
the same sizing math as the standalone window.
- Extract shared sizing into ExpandedPlayerWindowManager.fittedPlayerSize
and add fittedSheetSize for the sheet path.
- Add SheetWindowResizer (NSViewRepresentable) + .sheetWindowSize modifier
that resizes the hosting sheet window, since .presentationSizing(.fitted)
only fits once at presentation.
- Let the sheet content fill the window and paint the window background
black so animated resizes stay gap-free with no white bars.
c245a0e2a0