Get GraphRAG statistics

curl --request GET \
  --url https://api.case.dev/vault/{id}/graphrag/stats \
  --header 'Authorization: Bearer <token>'

{
  "entities": 1247,
  "relationships": 3521,
  "communities": 89,
  "documents": 156,
  "lastProcessed": "2024-01-15T10:30:00Z",
  "status": "completed"
}