Remove group categories from a published path's visibility

Body of POST and DELETE on /v2/published-paths/{id}/relationships/category-visibility/.

207 Multi-Status response envelope for batch-delete operations.

Distinct from BatchResultEnvelope so the generic T on the latter stays bound to a real resource type and consumers reading BatchSucceededItem.result keep their non-null contract.

Items appear in the same order as the request inputs. summary.succeeded counts BatchDeletedItem rows — the field name reflects "operation did not fail" rather than the verb-specific outcome (which is on every item's own status discriminator).