List categories

curl --request GET \
  --url https://api.marblecms.com/v1/categories \
  --header 'Authorization: Bearer <token>'

{
  "categories": [
    {
      "id": "clx456def",
      "name": "Technology",
      "slug": "technology",
      "description": "Tech news and tutorials",
      "count": {
        "posts": 15
      }
    }
  ],
  "pagination": {
    "limit": 10,
    "currentPage": 1,
    "nextPage": 2,
    "previousPage": null,
    "totalPages": 5,
    "totalItems": 42
  }
}