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/renderer/extensions/vueNodes/widgets/components/BatchNavigation.vue

@@ -0,0 +1,38 @@
+<template>
+  <div v-if="count > 1" class="flex items-center gap-1">
+    <span class="mr-1 text-muted-foreground">
+      <slot name="label" />
+    </span>
+    <Button
+      variant="muted-textonly"
+      size="icon-sm"
+      :disabled="index === 0"
+      data-testid="batch-prev"
+      @click="index--"
+    >
+      <i class="icon-[lucide--chevron-left]" />
+    </Button>
+    <span data-testid="batch-counter">
+      {{ $t('batch.index', { current: index + 1, total: count }) }}
+    </span>
+    <Button
+      variant="muted-textonly"
+      size="icon-sm"
+      :disabled="index === count - 1"
+      data-testid="batch-next"
+      @click="index++"
+    >
+      <i class="icon-[lucide--chevron-right]" />
+    </Button>
+  </div>
+</template>
+
+<script setup lang="ts">
+import Button from '@/components/ui/button/Button.vue'
+
+const index = defineModel<number>({ required: true })
+
+defineProps<{
+  count: number
+}>()
+</script>