- 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
