Improve/Add Controls to Refund Processing

🔍 Problem Statement

As a Pelcro admin, refund processing lacks flexibility — partial refunds are not supported (including on prepaid/advance invoices for future phases), refunds cannot be directed to a different method, and no internal note can be recorded. This forces refunds to be processed directly in the gateway, where they never produce a credit note and are not reflected in deferred revenue accounting.

💡 User Story

As a Pelcro admin, I want to issue partial refunds — on settled payments and on prepaid/advance invoices — with a refund destination and an internal note, so that I can handle every refund scenario in Pelcro while keeping accounting records accurate.

🎯 Definition of Done (DoD)

• ✔ Given a completed payment, when an admin initiates a refund, then they can specify a partial amount, select the refund destination, and add an internal note.
• ✔ Given a prepaid/advance invoice for a future phase, when an admin issues a partial refund, then it is accepted and the corresponding credit note and deferred revenue adjustment are created.
• ✔ This change will impact UI / API — specifically the payment/invoice detail pages (Platform UI) and the refund flow in the Core API.
• ✔ Limitations: total refunded cannot exceed the amount collected; refund destinations are limited to those supported by the underlying gateway.