Top-level categories. Use as the seed step for a BFS walk via
GET /locations/{locationId}/categories/{categoryId}.

Two integration patterns

1. Full dump — call GET /locations/{locationId}/catalogue once.
   Cheapest for small catalogues; the response can be large for big
   stores.
2. BFS walk — start from this endpoint (root categories) and
   recursively call category-details for each. Lets you parallelise
   and incrementally update.

Catalogue caveats

• Responses can be large for stores with thousands of products.
  Pick the BFS pattern for big catalogues; you can fan out
  concurrently across categories.
• Stock control is per online location — out_of_stock reflects
  availability at the merchant's configured stock locations. Don't
  cache it across locations.
• These endpoints are read-only and rate-limit-friendly — sync
  periodically (e.g. every 15 min) and after StoreTurnedOn webhooks.