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.
- Replace the full-width material overlay bar with a compact, centered
capsule (Apple Music style) via a macOS-specific macOSCapsuleLayout
- Extend glassBackground() to use real Liquid Glass on macOS 26 with a
material fallback on macOS 15-25 (mirrors the PlayerOverlayButton pattern)
- Remove the duplicate close button (close now comes only from the
configurable button set)
- Keep the capsule visible in the main window while the separate player
window is open (window mode), still hidden in sheet mode
