fix(GRO-876): wire up refund button in invoice detail modal

- Add stripePaymentIntentId and stripeRefundId to Invoice interface (types)
- Include both fields in the invoice list endpoint select (api)
- Show Refund button only when: status=paid, stripePaymentIntentId exists,
  stripeRefundId is null, and current user is manager
- Render "Refunded" badge on already-refunded invoices
- Full/partial refund dialog with amount input for partial

Co-Authored-By: Paperclip <noreply@paperclip.ing>

apps/api/src/routes/invoices.ts

@@ -102,6 +102,7 @@ invoicesRouter.get(
         paidAt: invoices.paidAt,
         notes: invoices.notes,
         stripePaymentIntentId: invoices.stripePaymentIntentId,
+        stripeRefundId: invoices.stripeRefundId,
         createdAt: invoices.createdAt,
         updatedAt: invoices.updatedAt,
       })