feat(api): add brand archive endpoint Adds POST /brands/{id}/archive and wires it as brands.archive. Archiving is permanent and moves the brand's products, live subscriptions, and product collections to the brand given by move_products_to, which must belong to the same business and must not itself be archived; the primary brand is a valid target. move_products_to may be omitted only when the brand holds no products and no live subscriptions. The response reports archived_at plus the counts of products, subscriptions, and collections moved. The primary brand cannot be archived (403) and re-archiving conflicts (409). Spec 1.112.13 -> 1.113.0. - #275