Convert bank statements for FreeAgent

The standard FreeAgent job is the gap before the bank feed: a company's first months, a switched bank account, a director's statement backlog at year-end. Converted statements fill that gap as OFX uploads — FreeAgent treats them like feed data, so explaining, rules and reconciliation all work normally.

Upload oldest-first so the account's history builds in order, and let the balance verification do the worrying: each statement had to reconcile against its own printed opening and closing balances before the file existed, so the uploaded months tie out to the statement figures.