feat(ui): integrate Nuxt UI and rebuild layout and login pages

Wrap application in UApp and apply base UI styles
Build responsive default layout with navigation and footer
Implement staff login form with validation and toast notifications
Restructure index page routing

app/layouts/default.vue

@@ -1,11 +1,37 @@
 <template>
-  <div>
-    <slot />
+  <div class="min-h-dvh bg-default text-default">
+    <header class="border-b border-default bg-default">
+      <UContainer class="flex items-center justify-between gap-4 py-6">
+        <UBadge
+          label="Event Ticket System"
+          color="neutral"
+          variant="soft"
+          class="rounded-full px-3 py-1 font-semibold"
+        />
+
+        <UButton
+          id="loginBtn"
+          :to="route.path.startsWith('/login') ? '/' : '/login'"
+          :label="route.path.startsWith('/login') ? 'Back' : 'Login'"
+          color="neutral"
+          :variant="route.path.startsWith('/login') ? 'outline' : 'solid'"
+          :icon="route.path.startsWith('/login') ? 'i-lucide-arrow-left' : 'i-lucide-lock-keyhole'"
+        />
+      </UContainer>
+    </header>
+
+    <UMain>
+      <slot />
+    </UMain>
+
+    <footer class="border-t border-default bg-default">
+      <UContainer class="py-5 text-center text-sm text-muted">
+        © 2026 DAP 60th Anniversary Committee. All rights reserved.
+      </UContainer>
+    </footer>
   </div>
 </template>
 
 <script lang="ts" setup>
-
+const route = useRoute()
 </script>
-
-<style></style>