feat: Show empty workflow dialog when entering app builder with no nodes (#9379)

## Summary

Prompts users to load a template or return to graph when entering
builder mode on an empty workflow

## Screenshots (if applicable)

<img width="627" height="275" alt="image"
src="https://github.com/user-attachments/assets/c1a35dc3-4e8f-4abd-95b9-2f92524e8ebf"
/>

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-9379-feat-Show-empty-workflow-dialog-when-entering-app-builder-with-no-nodes-3196d73d36508123b643ec893cd86cac)
by [Unito](https://www.unito.io)

src/components/builder/BuilderDialog.vue

@@ -13,6 +13,7 @@
         </h2>
       </div>
       <Button
+        v-if="showClose"
         variant="muted-textonly"
         class="-mr-1"
         :aria-label="$t('g.close')"
@@ -37,6 +38,10 @@
 <script setup lang="ts">
 import Button from '@/components/ui/button/Button.vue'
 
+const { showClose = true } = defineProps<{
+  showClose?: boolean
+}>()
+
 defineEmits<{
   close: []
 }>()