Get Bookkeeping Health

Returns the provider's scoring of the client's books — health percentage, issue count and value at risk per time bucket, plus activity figures — quality and activity combined in one response so a bucket selector needs no further calls. The bucket names are the provider's own strings and the two lists' bucket sets differ; join by duration and expect gaps. Served through a short server-side cache — 'retrievedAt' says when the figures were actually fetched.