Switch payment method filter to a static list with an "other" bucket

Per feedback, drop the dynamic /mypayments/methods lookup (wasn't
loading reliably) in favor of a static cash/card/eft/voucher/other
dropdown. Server-side normalization now folds any gateway-reported
method outside those four manual-entry values (apple_pay, google_pay,
yoco, etc.) into "other" instead of "card", both in the returned data
and in the filter query.

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

backend/src/routes/paymentRoutes.js

@@ -4,7 +4,6 @@ const {
   createPayment,
   getPayments,
   getUserPayments,
-  getUserPaymentMethods,
   getPaymentById,
   getPaymentsByRegistration,
   getPaymentsByEvent,
@@ -21,7 +20,6 @@ router.post('/', protect, supervisor, createPayment);
 router.post('/yoco-checkout', protect, createYocoCheckout);
 router.post('/yoco-checkout/send', protect, supervisor, sendPaymentLink);
 router.get('/mypayments', protect, getUserPayments);
-router.get('/mypayments/methods', protect, getUserPaymentMethods);
 router.get('/:id', protect, getPaymentById);
 router.get('/registration/:registrationId', protect, getPaymentsByRegistration);