Normalize user-facing payment method to cash/card/eft/voucher

Per feedback, stop trying to surface every gateway-reported wallet
type (apple_pay, google_pay, yoco, ...) as its own filter/display
value on the user payment history page. Both /mypayments and
/mypayments/methods now fold anything outside the four manual-entry
methods into "card", both in the returned data and in the filter
query, so Apple Pay/Google Pay payments show up under Card.

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

backend/API_DOCUMENTATION.md

@@ -240,7 +240,7 @@ For unauthenticated (guest) registration on events with `requiresAuth: false`:
 | POST | `/api/payments` | supervisor+ | Record manual payment (cash/EFT) |
 | POST | `/api/payments/yoco-checkout` | user+ | Initiate Yoco checkout; re-evaluates early-bird pricing first — returns `{ priceUpdated: true, newTotal }` if prices changed |
 | GET | `/api/payments/mypayments` | user+ | Own payments |
-| GET | `/api/payments/mypayments/methods` | user+ | Distinct `method` values present in the user's own payments |
+| GET | `/api/payments/mypayments/methods` | user+ | Normalized method options (cash/card/eft/voucher) present in the user's own payments |
 | GET | `/api/payments/:id` | user+ | Payment by ID |
 | GET | `/api/payments/registration/:registrationId` | user+ | Payments for a registration |
 | GET | `/api/payments` | supervisor+ | All payments |