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/lib/roles.ts

@@ -23,7 +23,7 @@ export const roles: Role[] = [
     name: 'Entwickler',
     description: 'Voller Zugriff auf alle Bereiche',
     icon: 'code',
-    visibleCategories: ['compliance-sdk', 'ai', 'infrastructure', 'education', 'communication', 'development', 'website'],
+    visibleCategories: ['compliance-sdk', 'ai', 'education', 'website'],
     color: 'bg-primary-100 border-primary-300 text-primary-700',
   },
   {
@@ -31,7 +31,7 @@ export const roles: Role[] = [
     name: 'Manager',
     description: 'Executive Uebersicht',
     icon: 'chart',
-    visibleCategories: ['compliance-sdk', 'communication', 'website'],
+    visibleCategories: ['compliance-sdk', 'website'],
     color: 'bg-blue-100 border-blue-300 text-blue-700',
   },
   {