Added primary evidence for China scheme links
Four primary sources linked to UnionPay, Discover and Diners Club scheme-market relationships.
Changelog
Card method, scheme and network hierarchy normalized
Visa, Mastercard, UnionPay, American Express, JCB and Diners Club now use one payment-method-to-scheme-to-network path. iDEAL and Wero remain payment methods; Pix and UPI are schemes.
