Remove default layout, migrate all pages to topnav

- Add layout: 'topnav' to all 27 pages that were using default layout
- Delete app/layouts/default.vue

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/pages/goods.vue

@@ -3,3 +3,9 @@
     <GoodsContent />
   </Section>
 </template>
+
+<script setup lang="ts">
+definePageMeta({
+  layout: 'topnav'
+})
+</script>