Create an 11-slide Slidev deck for the RetailOS product and business development team proposing a technology partnership with payment gateway PayGate. Keep the tone strategic and logical, not hype-driven: show the merchant problem, why PayGate is a strong fit, how the integration would work, the commercial upside for RetailOS, a realistic pilot plan, and the specific decision we want from RetailOS. Use the `default` theme, keep it presentation-ready, and include a Mermaid diagram only if it genuinely clarifies the integration flow.