docs: confirm Vulkan device enumeration and close the Bazzite setup check

vulkaninfo names GPU0 as the discrete RTX 5070 Ti (NVIDIA 615.78.08, API
1.4.351), with the RADV iGPU as GPU1 and llvmpipe as GPU2. Note the device
selection risk for the engine and mark the ROADMAP environment item done.

ROADMAP.md

@@ -8,7 +8,7 @@ Living roadmap for this project. This file is the single source of truth for cur
 
 Status detail in [Docs/setup.md](Docs/setup.md); workstation audit in [Docs/environment.md](Docs/environment.md); pins in [Docs/toolchain.md](Docs/toolchain.md).
 
-- [-] Update Bazzite using its supported mechanism; verify NVIDIA driver and Vulkan operation.
+- [x] Update Bazzite using its supported mechanism; verify NVIDIA driver and Vulkan operation.
 - [ ] Register an Epic account and accept the Unreal license; obtain a pinned Linux engine build or build from Epic's authorized source repository.
 - [ ] Validate Unreal runs on Bazzite before asset production (not an officially supported distribution).
 - [-] Install the engine-required compiler/SDK, Git, Git LFS, and an editor; use Distrobox for isolated CLI dependencies where useful.