Fix: Background Image fix for dark theme loading change. (#8292)

## Summary

The variable whose name implied it was just an image URL bundled other
background pieces.

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-8292-Fix-Background-Image-fix-for-dark-theme-loading-change-2f26d73d36508177ae7bc24ae3cb027b)
by [Unito](https://www.unito.io)

src/services/colorPaletteService.ts

@@ -222,10 +222,7 @@ export const useColorPaletteService = () => {
 
     const backgroundImage = settingStore.get('Comfy.Canvas.BackgroundImage')
     if (backgroundImage) {
-      rootStyle.setProperty(
-        '--bg-img',
-        `url('${backgroundImage}') no-repeat center /cover`
-      )
+      rootStyle.setProperty('--bg-img', `url('${backgroundImage}')`)
     } else {
       rootStyle.removeProperty('--bg-img')
     }