Confirm statement suggestions

Confirm every exact_suggestion of the statement's pending lines in one request, as evaluated when the request runs: link stored references and cheques, pay the named contact's open document (needs payments:write), and create own-account transfers that resolve both lines. Amount-and-date candidates are never confirmed. Returns the resolved lines and the skipped ones (changed, forbidden or refused) that stay pending. Replaying the Idempotency-Key returns the first result and creates nothing.