Import an affiliate network sales report (CSV body, Content-Type: text/csv; up to 5 MB)

Parameters: network (required: impact = Actions report, cj = Commission Detail, anything else = generic column mapping), optional currency for reports without one and store (store code) for rows whose click id is unknown and whose merchant name matches no store. Upserts by (network, transaction id): re-uploading updates status and amounts, never duplicates. The file is accepted or rejected as a whole (400 lists up to 20 row errors).