Combobox

Fluent 2-styled filterable select with shadcn-style composable APIs. Built on @base-ui/react's Combobox for portalled positioning, focus management, keyboard navigation and built-in filtering; the field matches the kit's Input (bottom brand-accent focus, Clear + chevron), the flyout uses Fluent shadow-16 elevation, and selected/highlighted items use CheckmarkRegular + brand-neutral accent states. Passes Base UI's `multiple` prop through for a future Multi Select.