feat(landing): Use central button tailwind variant

landing/app/pages/kontakt.vue

@@ -43,7 +43,7 @@
 
       <!-- Form section -->
       <div class="animate-fade-in-up" style="animation-delay: 150ms">
-        <div class="glass rounded-3xl p-8 sm:p-10 shadow-2xl">
+        <UCard variant="glass" :ui="{ root: 'rounded-3xl shadow-2xl', body: 'p-8 sm:p-10' }">
           <!-- Success state -->
           <Transition
             enter-active-class="transition-all duration-500 ease-out"
@@ -66,12 +66,10 @@
                 {{ $t('contact.success.message') }}
               </p>
               <div class="flex flex-col sm:flex-row gap-3 justify-center">
-                <UButton to="/" variant="outline" class="btn-outline-gradient">
-                  <UIcon name="i-lucide-home" class="w-4 h-4 mr-2" />
+                <UButton to="/" variant="gradientOutline" leading-icon="i-lucide-home">
                   {{ $t('contact.success.backToHome') }}
                 </UButton>
-                <UButton class="btn-gradient" @click="resetForm">
-                  <UIcon name="i-lucide-mail-plus" class="w-4 h-4 mr-2" />
+                <UButton variant="gradient" leading-icon="i-lucide-mail-plus" @click="resetForm">
                   {{ $t('contact.success.sendAnother') }}
                 </UButton>
               </div>
@@ -153,23 +151,17 @@
             </Transition>
 
             <!-- Submit button -->
-            <UButton
-              type="submit"
-              size="xl"
-              block
-              :loading="isLoading"
-              class="btn-gradient rounded-xl font-semibold shadow-lg shadow-primary-500/25"
-            >
+            <UButton type="submit" size="xl" block variant="gradient" :loading="isLoading" class="rounded-xl">
               <template v-if="isLoading">
-                <span>{{ $t('contact.form.sending') }}</span>
+                {{ $t('contact.form.sending') }}
               </template>
               <template v-else>
                 <UIcon name="i-lucide-send" class="w-5 h-5 mr-2" />
-                <span>{{ $t('contact.form.submit') }}</span>
+                {{ $t('contact.form.submit') }}
               </template>
             </UButton>
           </UForm>
-        </div>
+        </UCard>
 
         <!-- Trust indicators -->
         <div class="mt-8 flex flex-wrap justify-center gap-6 animate-fade-in-up" style="animation-delay: 300ms">