Order payment response clarifications

Order payment responses now document provider-specific payment details and hosted redirects.

Order payment responses now document pg_payment_info per provider type:
manual methods such as bank_transfer and cod return an empty object;
virtual account methods expose provider reference and account details;
QRIS responses expose QR data or a QR image payload; e-wallet, card, and
invoice methods may expose provider actions while the browser should use
payment_url for hosted redirects. Payment methods use canonical flat
values, including bank-specific virtual-account codes such as va_bca.