Read an assigned client's approved statement basis

The approved statement basis (#2911, J-355) is a reporting configuration an accountant records with a reason and an approval reference. It is distinct from the tax election (tax settings' accounting method) and from the book basis. The history is append-only: a correction is a new row naming the row it supersedes. effective is the row in force on asOf (today, UTC): the latest row with effectiveDate on or before it, by effectiveDate, then createdAt, then id, descending; null when none. The basis is metadata only: it never changes a figure or reportBasis, which comes only from the cash computation. Human accountants only; hidden from the service key.