feat(landing): Use central button tailwind variant

landing/app/pages/newsletter-bestaetigt.vue

@@ -15,7 +15,10 @@
 
     <div class="relative max-w-2xl mx-auto px-4 sm:px-6 lg:px-8 text-center">
       <!-- Success card -->
-      <div class="glass rounded-3xl p-10 sm:p-14 shadow-2xl animate-fade-in-up">
+      <UCard
+        variant="glass"
+        :ui="{ root: 'rounded-3xl shadow-2xl animate-fade-in-up', body: 'p-10 sm:p-14' }"
+      >
         <!-- Checkmark icon with animation -->
         <div class="relative mb-8">
           <div
@@ -47,16 +50,11 @@
 
         <!-- CTA Button -->
         <div class="animate-fade-in-up" style="animation-delay: 400ms">
-          <UButton
-            to="/"
-            size="xl"
-            class="btn-gradient rounded-xl font-semibold shadow-lg shadow-primary-500/25 hover:shadow-primary-500/40 transition-shadow"
-          >
-            <UIcon name="i-lucide-home" class="w-5 h-5 mr-2" />
+          <UButton to="/" size="xl" variant="gradient" leading-icon="i-lucide-home" class="px-8 py-4">
             {{ $t('newsletterConfirmed.backToHome') }}
           </UButton>
         </div>
-      </div>
+      </UCard>
 
       <!-- Trust indicators -->
       <div class="mt-8 flex flex-wrap justify-center gap-6 animate-fade-in-up" style="animation-delay: 500ms">