Mark paid refused for provider orders

Symptoms

• "Tandai Lunas" fails on a QRIS/VA/Midtrans order
• A provider-payment order cannot be marked paid manually

Likely causes

• `POST /api/orders/:id/payment/mark-paid` only accepts MANUAL payment methods — it deliberately refuses provider/Midtrans methods so it never fakes the gateway status

How to fix

• For provider methods, let the Midtrans webhook mark it paid
• Manual mark-paid is only for manual methods (manual transfer/COD)
• Use `{ unpaid: true }` to reverse a manual mark-paid