Duplicate a financial transaction inside the SAME title. The copy is created as PENDING with a new code (FCP-/FCR- according to the type), no effected date and no installment number (the clone does not take part in the original numbering), keeping title, type and origin from the original. The request body is OPTIONAL: when absent the editable fields (dueDate, amount, paymentMethod, bankAccountId, description) are copied from the original (exact copy); when present each non-null field overrides the original's value field by field (a null field falls back to the original) and bankAccountId is resolved (404 when not found). A transaction in any status can be cloned. The parent title's balance is recalculated as the sum of its PENDING transactions (including the clone) and a PAID or CANCELLED title returns to PENDING.