UI Node with absolute position seems to be incorrectly scaled

## Bevy version

0.15.3

## \[Optional\] Relevant system information

- Mac M2

If your bug is rendering-related, copy the adapter info that appears when you run Bevy.

```ignore
2025-04-18T21:29:44.996370Z INFO bevy_diagnostic::system_information_diagnostics_plugin::internal: SystemInfo { os: "MacOS 15.3.1 ", kernel: "24.3.0", cpu: "Apple M2", core_count: "8", memory: "24.0 GiB" }
2025-04-18T21:29:45.084210Z INFO bevy_render::renderer: AdapterInfo { name: "Apple M2", vendor: 0, device: 0, device_type: IntegratedGpu, driver: "", driver_info: "", backend: Metal }
2025-04-18T21:29:45.248183Z INFO bevy_winit::system: Creating new window "App" (0v1#4294967296)
```

## What you did

I spawn a crosshair image using the following code:

```rs
pub fn spawn_crosshair(mut commands: Commands, window_query: Query<&Window, With>) {
if let Ok(window) = window_query.get_single() {
let crosshair_size = 8.0;
commands
.spawn(Node {
width: Val::Percent(100.0),
height: Val::Percent(100.0),
..default()
})
.with_children(|p| {
p.spawn((
ImageNode::solid_color(Color::srgb(0., 1., 0.)),
Node {
width: Val::Px(crosshair_size),
height: Val::Px(crosshair_size),
position_type: PositionType::Absolute,
left: Val::Px(window.width() / 2.0 - (crosshair_size / 2.0)),
top: Val::Px(window.height() / 2.0 - (crosshair_size / 2.0)),
..default()
},
));
});
}
}
```

## What went wrong

If it's not clear, break this out into:

- Crosshair (square) should appear at the center of the window
- Crosshair actually appear at lower-right corner
- If I divide the width and height by 4, crosshair appear at the center
- However, scaling factor is reported to be 1. Physical width/height are also same as logical.
- If I use percentage instead of absolute size, positioning is correct.

Start with the spawn_crosshair entry point and reproduce the behavior on Bevy 0.15.3 using the supplied absolute-position and percentage-position examples. Read the UI Node layout and window sizing behavior involved in absolute positioning; done means the 8px crosshair is centered with absolute pixel offsets without requiring division by four.

Written by the indexing model from the issue text.