feat: add Base UI Tailwind component library

Add composable wrappers for 37 Base UI component families.

Expose primitive and convenience APIs with shared styling utilities.

Add the registry manifest, installer CLI, generation and export checks.

Include a smoke example covering primitive and shadcn-style imports.

src/components/ui/combobox/item.tsx

@@ -0,0 +1,26 @@
+"use client"
+
+import * as React from "react"
+import { Combobox as BaseCombobox } from "@base-ui/react/combobox"
+import { cn } from "@/lib/utils"
+
+export type ComboboxItemProps = React.ComponentPropsWithoutRef<typeof BaseCombobox.Item> & {
+  className?: string
+}
+
+const BaseComboboxItem = BaseCombobox.Item as React.ElementType
+
+export const ComboboxItem = React.forwardRef<HTMLElement, ComboboxItemProps>(
+  ({ className, ...props }, ref) => (
+    <BaseComboboxItem
+      ref={ref}
+      className={cn(
+        "grid cursor-default grid-cols-[1rem_1fr] items-center gap-2 p-2 text-sm leading-4 outline-none select-none data-highlighted:relative data-highlighted:z-0 data-highlighted:text-white data-highlighted:before:absolute data-highlighted:before:inset-0 data-highlighted:before:z-[-1] data-highlighted:before:bg-neutral-950 dark:data-highlighted:text-neutral-950 dark:data-highlighted:before:bg-white",
+        className,
+      )}
+      {...props}
+    />
+  ),
+)
+
+ComboboxItem.displayName = "ComboboxItem"