fix(public): do not expose coupon code after preregistration

Codes are still created and stored for Mailwizz; JSON response omits
coupon_code. Thank-you UI explains email delivery instead of showing code.

Made-with: Cursor

resources/views/public/page.blade.php

@@ -71,7 +71,6 @@
                     'redirectUrl' => filled($redirectAfterSubmit) ? $redirectAfterSubmit : null,
                     'strings' => [
                         'linkCopied' => __('Link gekopieerd!'),
-                        'couponCopied' => __('Kortingscode gekopieerd!'),
                         'redirectCountdown' => __('You will be redirected in :seconds s…'),
                     ],
                 ]))"