Consolidate Kreditkarte/PayPal into one "Online-Zahlung" checkout option

Both already route through the same Stripe PaymentIntent
(automatic_payment_methods: enabled — Stripe's own recommended Payment
Element pattern, letting Stripe itself decide which eligible method to
show). Pre-selecting one of two identical-behind-the-scenes rows before
the payment step was redundant friction, not a real choice. Collapses
them into one option with a hint text explaining the actual instrument
is picked on the next screen; Überweisung is unaffected.

Also refines paymentMethodTitle from a neutral "Online-Zahlung"
placeholder (snapshotted at order-creation time, before the customer has
picked an instrument) to the real one Stripe reports, once payment
confirms — carried through to both the stored order and the
sessionStorage snapshot shown on /bestellbestaetigung.

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

app/checkout/verarbeitung/VerarbeitungContent.tsx

@@ -45,7 +45,14 @@ export function VerarbeitungContent() {
           try {
             const pending = window.sessionStorage.getItem(PENDING_ORDER_KEY);
             if (pending) {
-              window.sessionStorage.setItem(ORDER_KEY, pending);
+              // Patch in the real instrument (Kreditkarte/PayPal) now
+              // that it's known — the pending snapshot was written at
+              // checkout submission time with the neutral "Online-
+              // Zahlung" placeholder, before the customer had actually
+              // picked one on the Payment Element.
+              const snapshot = JSON.parse(pending);
+              if (data.paymentMethodTitle) snapshot.paymentMethodTitle = data.paymentMethodTitle;
+              window.sessionStorage.setItem(ORDER_KEY, JSON.stringify(snapshot));
               window.sessionStorage.removeItem(PENDING_ORDER_KEY);
             }
           } catch {