feat: add batch image navigation to ImageCompare node (#9151)

## Summary

Add batch image navigation to the ImageCompare node so users can browse
all images in a batch instead of only seeing the first one.
## Changes
The backend already returns all batch images in a_images/b_images
arrays, but the frontend only used index [0]. Now all images are mapped
to URLs and a navigation bar with prev/next controls appears above the
comparison slider when either side has more than one image. A/B sides
navigate independently. Extracted a reusable BatchNavigation component
for the index selector UI.

fix https://github.com/Comfy-Org/ComfyUI_frontend/issues/9098

## Screenshots (if applicable)


https://github.com/user-attachments/assets/a801cc96-9182-4b0d-a342-4e6107290f47

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-9151-feat-add-batch-image-navigation-to-ImageCompare-node-3116d73d365081498be6d401773619a3)
by [Unito](https://www.unito.io)

src/extensions/core/imageCompare.ts

@@ -26,22 +26,18 @@ useExtensionService().registerExtension({
       const { a_images: aImages, b_images: bImages } = output
       const rand = app.getRandParam()
 
-      const beforeUrl =
-        aImages && aImages.length > 0
-          ? api.apiURL(`/view?${new URLSearchParams(aImages[0])}${rand}`)
-          : ''
-      const afterUrl =
-        bImages && bImages.length > 0
-          ? api.apiURL(`/view?${new URLSearchParams(bImages[0])}${rand}`)
-          : ''
+      const toUrl = (params: Record<string, string>) =>
+        api.apiURL(`/view?${new URLSearchParams(params)}${rand}`)
+
+      const beforeImages =
+        aImages && aImages.length > 0 ? aImages.map(toUrl) : []
+      const afterImages =
+        bImages && bImages.length > 0 ? bImages.map(toUrl) : []
 
       const widget = node.widgets?.find((w) => w.type === 'imagecompare')
 
       if (widget) {
-        widget.value = {
-          before: beforeUrl,
-          after: afterUrl
-        }
+        widget.value = { beforeImages, afterImages }
         widget.callback?.(widget.value)
       }
     }