feat(topbar): change environment prop from string to ReactNode

Allows consuming apps to pass a custom dropdown or any interactive
element instead of a static string label. Rendering changed from
<span> to <div> to support block-level children.

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

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

@@ -1,3 +1,4 @@
+import { type ReactNode } from 'react'
 import { Search, Moon, Sun, Power } from 'lucide-react'
 import styles from './TopBar.module.css'
 import { Breadcrumb } from '../../composites/Breadcrumb/Breadcrumb'
@@ -14,7 +15,7 @@ import type { BreadcrumbItem } from '../../providers/BreadcrumbProvider'
 
 interface TopBarProps {
   breadcrumb: BreadcrumbItem[]
-  environment?: string
+  environment?: ReactNode
   user?: { name: string }
   onLogout?: () => void
   className?: string
@@ -102,7 +103,7 @@ export function TopBar({
           {theme === 'light' ? <Moon size={16} /> : <Sun size={16} />}
         </button>
         {environment && (
-          <span className={styles.env}>{environment}</span>
+          <div className={styles.env}>{environment}</div>
         )}
         {user && (
           <Dropdown