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

Cherry-pick of 628ed34 to fix @typescript-eslint/no-unused-vars
error on PR #351 Lint & Typecheck.

The issueRefund function was defined but never called. This commit:
- Removes the inline async onClick handler that bypassed issueRefund
- Wires the Refund button to open setShowRefundDialog(true) instead
- Uses issueRefund function (with refundAmount/refundError/refunding state)
- Adds manager role check before showing refund button
- Shows "Refunded" badge when invoice.stripeRefundId is set

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,
       })