Clear Card 1's email field when switching away from the login prompt

"Andere E-Mail-Adresse verwenden" only hid the inline login prompt
before, leaving the already-registered address still sitting in the
field — the shopper had to manually select/delete it before typing a
new one. Now clears email + loginPassword + the email field's error
alongside dismissing the prompt.

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

app/checkout/components/CheckoutContent.tsx

@@ -803,6 +803,15 @@ export function CheckoutContent({
                     onClick={() => {
                       setShowLogin(false);
                       setLoginError(null);
+                      // Clears Card 1's own email field too, not just the
+                      // login prompt — leaving the already-registered
+                      // address sitting there meant the shopper had to
+                      // manually select/delete it before typing a new one.
+                      // Password cleared alongside it since it was only
+                      // ever meaningful for the email that's now gone.
+                      setEmail("");
+                      setLoginPassword("");
+                      setFieldError("email", "");
                     }}
                     className="text-label text-text-muted underline hover:text-text-primary transition-colors"
                   >