example "First person view model" do not render default layer

## Bevy version and features

```
bevy = { version = "0.17.2", default-features = false, features = [
"std",
"zstd_rust",
"async_executor",
"android-game-activity",
"android_shared_stdcxx",
"animation",
"bevy_asset",
"bevy_audio",
"bevy_color",
"bevy_core_pipeline",
"bevy_gilrs",
"bevy_gizmos",
"bevy_gltf",
"bevy_input_focus",
#"bevy_log",
"bevy_mesh_picking_backend",
"bevy_pbr",
"bevy_picking",
"bevy_render",
"bevy_scene",
"bevy_sprite",
"bevy_sprite_picking_backend",
"bevy_state",
"bevy_text",
"bevy_ui",
"bevy_ui_picking_backend",
"bevy_window",
"bevy_winit",
"custom_cursor",
"default_font",
"hdr",
"multi_threaded",
"png",
"smaa_luts",
"sysinfo_plugin",
"tonemapping_luts",
"vorbis",
"webgl2",
#"x11",
"wayland",
] }
```

## \[Optional\] Relevant system information

Probably not relevant, but for completeness:
Rust 1.90, Kubuntu 25.04, Vulkan backend, NVIDIA RTX 5080 (driver 580.82.09)

## What you did

Ran the official example
[https://bevy.org/examples/camera/first-person-view-model/](https://bevy.org/examples/camera/first-person-view-model) using Bevy 0.17.2.

## What went wrong

When running the example, the DEFAULT_RENDER_LAYER is not rendered — only the VIEW_MODEL_RENDER_LAYER is visible.

## Additional information

Adding `clear_color: ClearColorConfig::None` to the view-model camera fixes the problem:

```
parent.spawn((
Camera3d::default(),
Camera {
// Bump the order to render on top of the world model.
order: 1,
clear_color: ClearColorConfig::None, // <-- herer
..default()
},
Projection::from(PerspectiveProjection {
fov: 70.0_f32.to_radians(),
..default()
}),
// Only render objects belonging to the view model.
RenderLayers::layer(VIEW_MODEL_RENDER_LAYER),
));
```

It works after that, but I'm not sure if this is the correct way to fix it.