[test] fix flaky Vue upload widget browser tests using randomize url param (#5845)

## Summary

Fix browser tests that use filenames in loader nodes. When the files
don't exist, the fallback/error component shows the request URL which
contains random cache-busting param which makes tests fail due to
non-deterministic nature.


[Context](https://github.com/Comfy-Org/ComfyUI_frontend/pull/5831#discussion_r2386582256)

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-5845-test-fix-flaky-Vue-upload-widget-browser-tests-using-randomize-url-param-27d6d73d36508107a0d0d52d2764a028)
by [Unito](https://www.unito.io)

---------

Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: github-actions <github-actions@github.com>

src/renderer/extensions/vueNodes/components/ImagePreview.vue

@@ -20,7 +20,9 @@
       >
         <i-lucide:image-off class="w-12 h-12 mb-2 text-gray-400" />
         <p class="text-sm text-gray-300">{{ $t('g.imageFailedToLoad') }}</p>
-        <p class="text-xs text-gray-400 mt-1">{{ currentImageUrl }}</p>
+        <p class="text-xs text-gray-400 mt-1">
+          {{ getImageFilename(currentImageUrl) }}
+        </p>
       </div>
 
       <!-- Loading State -->
@@ -260,4 +262,12 @@ const handleKeyDown = (event: KeyboardEvent) => {
       break
   }
 }
+
+const getImageFilename = (url: string): string => {
+  try {
+    return new URL(url).searchParams.get('filename') || 'Unknown file'
+  } catch {
+    return 'Invalid URL'
+  }
+}
 </script>