Runs a single full-text query over the indexed entities and returns matches grouped by
entity type. Requires an authenticated token; results are scoped by the calling user's
permissions. This GET form takes its parameters from the query string and is convenient for
simple, link-shareable searches; the POST form accepts the same shape in the request body and
is preferred when filters get large.

Searchable entities are the SearchEntity values (e.g. AffiliateProgram,
Brand, BrandLink, AffiliateProgramAccount, TrafficSource); use
documentTypes to restrict the search to specific ones.

Pagination uses offset/limit (0-based offset). Alternatively set
limitPerCategory to return up to N results per entity type (mutually exclusive with
limit). Sort with sortBy (Relevance, CreatedAt, UpdatedAt) and sortOrder
(Ascending, Descending); the default is relevance ranking.