Child node with width and height has a blank computed node

## Bevy version

0.16.1

## \[Optional\] Relevant system information
cargo 1.87.0 (99624be96 2025-05-06)
Ubuntu 24.04.2 LTS

## What you did

I've made an image node with an entry pannel node under it that will contain nodes for all the entries in the folder. The nodes spawn but they don't show as the entry pannel get a blank computed node for some reason. To make sure that the entry pannel works, in the egui inspector, I gave it a background colour and a size but still nothing.

https://github.com/user-attachments/assets/9fe44fbc-93a9-4671-9b0f-b4ff7124f1cc

Repo: https://github.com/GalaMana/bevy_river_level_editor

Thanks a lot if you can help!

Start by reproducing the layout in the linked bevy_river_level_editor repository with Bevy 0.16.1, then inspect the image node, entry panel node, and child nodes in the egui inspector. Check why the entry panel receives a blank computed node despite having width, height, and a background color. Done means identifying the cause and confirming that the entry panel and its spawned children render correctly.

Written by the indexing model from the issue text.