feat: add userMenuItems prop to TopBar and export DropdownItem type

Allows consumers to inject custom menu items above the Logout action
in the user dropdown. Items are separated from Logout by a divider.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/design-system/composites/index.ts

@@ -13,6 +13,7 @@ export type { Column, DataTableProps } from './DataTable/types'
 export { DetailPanel } from './DetailPanel/DetailPanel'
 export { EntityList } from './EntityList/EntityList'
 export { Dropdown } from './Dropdown/Dropdown'
+export type { DropdownItem } from './Dropdown/Dropdown'
 export { EventFeed } from './EventFeed/EventFeed'
 export { GroupCard } from './GroupCard/GroupCard'
 export { KpiStrip } from './KpiStrip/KpiStrip'

src/design-system/layout/TopBar/TopBar.tsx

@@ -17,6 +17,7 @@ interface TopBarProps {
   breadcrumb: BreadcrumbItem[]
   environment?: ReactNode
   user?: { name: string }
+  userMenuItems?: import('../../composites/Dropdown/Dropdown').DropdownItem[]
   onLogout?: () => void
   className?: string
 }
@@ -32,6 +33,7 @@ export function TopBar({
   breadcrumb,
   environment,
   user,
+  userMenuItems,
   onLogout,
   className,
 }: TopBarProps) {
@@ -114,6 +116,8 @@ export function TopBar({
               </div>
             }
             items={[
+              ...(userMenuItems ?? []),
+              ...(userMenuItems?.length ? [{ label: '', divider: true }] : []),
               { label: 'Logout', icon: <Power size={14} />, onClick: onLogout },
             ]}
           />