Add a CI screenshot run for the tonemapping example

[stuartparmenter]

Objective

The tonemapping example never runs in CI, and it's the most direct coverage for upcoming tonemapping render-path work.

Solution

Add the tonemapping example to the Pixel Eagle tests.

Testing

Tested locally with lavapipe to validate the run and the screenshot.

---

This PR was built by me with the assistance of Claude Code w/ Fable 5

[stuartparmenter]

I would also be fine removing this once I finish making my way through all the PRs, or we can skip it entirely if people prefer keeping CI lighter

[mockersf]

This example doesn't work on Windows in CI

     Running `target\release\examples\tonemapping.exe`
2026-08-20T03:46:08.901828Z  INFO bevy_diagnostic::system_information_diagnostics_plugin::internal: SystemInfo { os: "Windows Server 2025 Datacenter", kernel: "26100", cpu: "AMD EPYC 7763 64-Core Processor", core_count: "2", memory: "16.0 GiB" }
2026-08-20T03:46:09.024235Z  INFO bevy_render::renderer: AdapterInfo { name: "Microsoft Basic Render Driver", vendor: 5140, device: 140, device_type: Cpu, device_pci_bus_id: "", driver: "10.0.26100.33158", driver_info: "", backend: Dx12, subgroup_min_size: 4, subgroup_max_size: 4, transient_saves_memory: Some(false), limit_bucket: None }
2026-08-20T03:46:09.024302Z  WARN bevy_render::renderer: The selected adapter is using a driver that only supports software rendering. This is likely to be very slow. See https://bevy.org/learn/errors/b0006/
2026-08-20T03:46:09.186623Z  INFO bevy_pbr::cluster: GPU clustering is supported on this device.
2026-08-20T03:46:09.186744Z  INFO bevy_render::batching::gpu_preprocessing: GPU preprocessing is fully supported on this device.
2026-08-20T03:46:09.187670Z  INFO bevy_winit::system: Creating new window tonemapping (67v0)
2026-08-20T03:50:57.985322Z  INFO bevy_dev_tools::ci_testing::systems: Took a screenshot at frame 400.
2026-08-20T03:53:34.951689Z ERROR bevy_render::error_handler: Caught DeviceLost error: Unknown Out of memory
2026-08-20T03:53:34.951759Z ERROR bevy_render::error_handler: Caught rendering error: Out of Memory
2026-08-20T03:53:34.953689Z ERROR bevy_render::error_handler: Caught rendering error: Validation Error

Caused by:
  In Buffer::map_async
    Buffer with 'clustering metadata staging buffer' label is invalid

2026-08-20T03:53:34.954013Z ERROR bevy_render::error_handler: Quitting the application due to DeviceLost RenderError

[stuartparmenter]

This example doesn't work on Windows in CI

weird, I'll try to debug why it is running out of memory

[mockersf]

It would probably be easier to add a simple testbed that use less memory?

Anyway using a testbed for regressions would be better than using the example in CI

[alice-i-cecile]

Putting something like this into the testbed makes more sense, agreed.

[stuartparmenter]

thanks, I'll review a few options here