refactor(admin-v2): Rename to Admin Lehrer KI and remove migrated categories

Remove communication, infrastructure, and development categories from
navigation (now in Admin Core on port 3008). Rename Admin v2 to
Admin Lehrer KI in sidebar, header, and browser title.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

admin-v2/app/layout.tsx

@@ -5,7 +5,7 @@ import './globals.css'
 const inter = Inter({ subsets: ['latin'] })
 
 export const metadata: Metadata = {
-  title: 'BreakPilot Admin v2',
+  title: 'BreakPilot Admin Lehrer KI',
   description: 'Neues Admin-Frontend mit verbesserter Navigation und Rollen-System',
 }