PosTransactionDto specification — field reference for transaction data

A complete field reference for PosTransactionDto, the canonical model for the transaction data ReceiptRoller handles. For each category — identifiers, dates, amounts, line items, payments, staff, status, and CRM linkage — it summarizes the field names, types, meanings, and how each POS vendor populates them. A reference for developers and external-system integrators. Also referenced from the Smaregi and Square mapping articles.