fix: image compare height mismatch between before and after images (#7931)

## Summary

Add relative and size-full classes to the inner container div to ensure
both images share the same positioning context and size constraints.

fix https://github.com/Comfy-Org/ComfyUI_frontend/issues/7928

## Screenshots (if applicable)
before
<img width="666" height="369" alt="image"
src="https://github.com/user-attachments/assets/2118685c-412a-4689-aac4-c0e592e47678"
/>

after
<img width="500" height="505" alt="image"
src="https://github.com/user-attachments/assets/c773147a-a28a-4145-a26a-6f19dafad50f"
/>

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-7931-fix-image-compare-height-mismatch-between-before-and-after-images-2e36d73d365081b69b49dfdd63d242a9)
by [Unito](https://www.unito.io)

src/renderer/extensions/vueNodes/widgets/components/WidgetImageCompare.vue

@@ -1,6 +1,6 @@
 <template>
   <div ref="containerRef" class="relative size-full min-h-32 overflow-hidden">
-    <div v-if="beforeImage || afterImage">
+    <div v-if="beforeImage || afterImage" class="relative size-full">
       <img
         v-if="afterImage"
         :src="afterImage"