Apply payment method normalization consistently across user-facing views

Audited every place Payment.method reaches the UI. The main user
dashboard's per-registration payment list (fed by GET
/api/payments/registration/:id) was still showing the raw gateway
string, since that endpoint is shared with the staff-facing supervisor
payments page and wasn't touched by the earlier /mypayments fix.

Extracted the cash/card/eft/voucher/other normalization (matching
normalizeUserMethod on the backend) into frontend/src/lib/paymentMethod.ts
and applied it to both user-facing payment displays. Staff-facing views
(supervisor payments, at-the-door, reports, cashup) intentionally keep
showing the raw method for reconciliation and were left unchanged.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

frontend/src/app/dashboard/user/page.tsx

@@ -4,6 +4,7 @@ import { useAuth } from "@/hooks/useAuth";
 import { apiFetch } from "@/lib/api";
 import { useRouter } from "next/navigation";
 import { formatDate } from "@/lib/date";
+import { formatPaymentMethod } from "@/lib/paymentMethod";
 import { QrImage } from "@/components/shared/QrImage";
 
 // Helper formatters
@@ -1008,7 +1009,7 @@ export default function UserDashboardPage() {
                   <div className="font-medium mb-1">Payments</div>
                   <ul className="text-sm list-disc pl-5 space-y-1">
                     {activeBill.payments.map((p: any) => (
-                      <li key={p.id}>{new Date(p.createdAt).toLocaleString()} — {formatRand(p.amount)} ({p.method || "Payment"})</li>
+                      <li key={p.id}>{new Date(p.createdAt).toLocaleString()} — {formatRand(p.amount)} ({formatPaymentMethod(p.method)})</li>
                     ))}
                   </ul>
                 </div>