feat: implement dLocal redirect payins for emerging markets

[teesofttech]

Why

dLocal offers payins across emerging markets with local payment methods and supports redirect payment flows that fit PayBridge hosted checkout.

Official docs:

• https://docs.dlocal.com/
• https://docs.dlocal.com/reference/create-payment

Scope

• Begin with REDIRECT flow; do not collect raw card data inside PayBridge.
• Implement signed authentication, country/payment-method selection, create, status, refund, and notifications.
• Model country as a required routing input where dLocal requires it.
• Respect currency decimal rules that vary by country.

Acceptance criteria

• Authentication signing has deterministic test vectors.
• Country/currency/payment-method validation happens before the API call.
• Unit fixtures cover redirect, pending, paid, declined, refund, signature failure, and malformed response.
• Sandbox integration tests include negative cases.
• Direct card endpoints are explicitly out of scope until PCI implications are reviewed.
• Capability docs list verified countries rather than claiming global coverage.