Sheets that keep the platform behaviour and none of the platform paint

ModalBottomSheet is worth keeping for what it does off screen — drag-to-dismiss, the scrim, back handling, staying above the keyboard. What it paints is worth replacing wholesale, and once a codebase has a dozen sheets the replacement has to be one shape, not twelve.

// adapted: colour tokens renamed, content elided
val sheetState = rememberModalBottomSheetState(skipPartiallyExpanded = true)