Lister les collections

{
  "data": [
    {
      "id": "col_abc123xyz",
      "name": "Ma Collection",
      "slug": "ma-collection",
      "is_active": true,
      "created_at": "2026-01-15T10:30:00Z",
      "expires_at": "2026-12-31T23:59:59Z",
      "description": "Description courte",
      "allow_download": true
    }
  ],
  "object": "list"
}