Replace raw `animate-pulse bg-muted` divs with the `<Skeleton>` component
across all major page and section skeletons. Every loading state now uses
the premium sweeping shimmer animation instead of the basic pulse.
Files: TrackDetailPageSkeleton, LibraryPageSkeleton, PlaylistDetailPageSkeleton,
DiscoverViewSkeleton, PlaybackDashboardSkeleton, StudioViewSkeleton,
MonitoringDashboardSkeleton, LibraryManagerSkeleton, UploadViewSkeleton,
FileManagerViewSkeleton, TrackSearchFiltersSkeleton, TrackListPaginationSkeleton,
TrackFiltersSkeleton, TrackHistorySkeleton, PlaylistActionsSkeleton, TrackGrid.
Co-authored-by: Cursor <cursoragent@cursor.com>
333aeee226