Bulk Action Bar

The component is self-contained: one file, no dependencies, the palette in --vibeui-datagrid-002-*. A client component: useState holds the list of selected ids. The header checkbox gets indeterminate through a ref callback — this state cannot be set from markup. The action bar occupies the same place as the ordinary header and keeps a min-height, so the rows do not jump at the very first tick. The counter of what is selected is declared aria-live=polite and shows the total straight away — that total is usually the reason rows are selected at all. A selected row is marked both by a fill and by a stripe on the left through an inset box-shadow: a fill alone is not enough next to a hovered row. Every row checkbox has its own aria-label carrying the client name. The theme comes from the surrounding color-scheme through light-dark(): by default the grid lays no panel under itself, it sits on the page background, while the background prop switches on a panel of its own.