Upgrade Base UI to 1.9.0

Base UI 1.9.0 is out (release notes). It lists no breaking changes. It needs @base-ui/utils 0.5.0.

Do this after the open Base UI PRs merge (#946, #948 to #961, #963), so the upgrade does not conflict with them.

Upgrade PR

Bump @base-ui/react to ~1.9.0 and @base-ui/utils to ~0.5.0.
Accordion and Collapsible triggers now get the native disabled attribute. Our .accordion-trigger:disabled and .trigger:disabled styles did not apply before and will apply now. Check that disabled triggers look right.
Autocomplete passes the originating event to onItemHighlighted, and typing reports the reason none. Check our handlers in menu/menu-content.tsx and context-menu/context-menu-content.tsx.
Combobox and Select accept readonly arrays for multiple values. Let our wrapper types accept readonly string[] too.
ScrollArea drops the viewport role. Update any tests that rely on it.

Menu filtering: Menu.FilterProvider, Menu.Input, and onItemHighlighted (preview). Our searchable Menu and ContextMenu combine Base UI Autocomplete with Menu. Moving to Base UI's own menu filtering could simplify both, and the item counter in Use one item counter for Combobox, Menu, and Command #962. Wait until it leaves preview, or try it on a branch first.
eventDetails.preventUnmountOnClose() for Select, Combobox, and Autocomplete keeps the popup mounted after it closes. It could make the hidden registration pass in Select lighter. It does not cover the first open, so the pass is still needed.
Use the new CssVariables and DataAttributes type exports in the docs props.ts files.

Combobox: stale chip focus after returning to the input (feat: [combobox] use base ui chips, clear, empty, and status #954).
Drawer: virtual keyboard spacing, iOS focus, swipe velocity, and x/y options for data-base-ui-swipe-ignore (feat: [drawer] add swipe area, keyboard handling, and indent #956).
Item registration stays in sync under Strict Mode, and large lists mount faster (Select and Combobox).