refactor: Replace UCard with header tag in admin page

pages/admin.vue

@@ -1,7 +1,7 @@
 <template>
   <div class="min-h-screen bg-gray-100">
     <!-- Header -->
-    <UCard class="rounded-none" :ui="{ body: { padding: 'py-2 px-4 sm:px-6 lg:px-8' } }">
+    <header class="bg-white shadow-sm border-b py-2 px-4 sm:px-6 lg:px-8">
       <div class="flex justify-between items-center">
         <div class="flex items-center space-x-4">
           <img src="/logos/logo.png" alt="New Life Christian Church" class="h-10" />
@@ -23,7 +23,7 @@
           Logout
         </UButton>
       </div>
-    </UCard>
+    </header>
 
     <UContainer class="py-8">
       <UCard>