Senior Full-Stack Developer for Fintech Prototype

We are developing a functional prototype of a B2B fintech platform focused on treasury and financial operations for SMEs. We need one senior, part-time, full-stack developer to build the prototype until our future full-time CTO becomes available. The developer must build the system in a clean, documented, and transferable way so the CTO can take over without major rebuilding. The prototype will include company and user accounts, roles and permissions, cash visibility, transaction uploads, working-capital information, cash-flow forecasting, approvals, audit trails, and a simulated payment workflow. It will initially use dummy or sandbox data and will not process real customer funds. We want to begin with a short trial or discovery stage before confirming the complete prototype engagement.