Create the paid invoice for one bank credit the importer did not book

The manual override for /invoices/import. Every credit the import left uncreated — unclassified (the model was unsure) and nonInvoiceable (it judged the credit not to be revenue) — comes back with a ready-made payload under details; post that object here verbatim to create the invoice anyway, optionally overriding clientName and itemName first. The invoice is built by the importer's own builder: stored paid, payment recorded on the transaction date, VAT inclusive, and carrying the same importRef, so a later re-import of the statement recognises it. Confirming the same credit twice returns the first invoice (alreadyExisted: true) instead of creating a second.