* Studio: defer the Windows CUDA Toolkit check so prebuilt users are not blocked
setup.ps1 section 1e validated the installed CUDA Toolkit against the driver in
Phase 1 and hard-exited when the toolkit was newer than the driver supports.
That ran before the prebuilt llama.cpp install (Phase 3.4), which is
self-contained and needs no local toolkit. A Blackwell host (sm_120) on a driver
that advertises CUDA 13.2 with CUDA Toolkit 13.3 installed was blocked entirely,
even though the prebuilt selector would have given it a working GPU build.
The toolkit (nvcc) is only consumed by the Phase 4 source build. Move section 1e
into a Resolve-CudaToolkit function and call it lazily at the source-compile
branch, gated on $HasNvidiaSmi. The prebuilt path no longer touches the toolkit;
forced/source builds keep the identical requirement, winget auto-install, and
error text via -RequireOrExit.
Add a pwsh unit test that extracts the real function and runs it against a
spoofed Blackwell sm_120 / driver 13.2 / toolkit 13.3 host: the prebuilt path
defers, the forced build still fails fast.
Refs #5879.
* Studio: correct a stale Phase-1 prerequisites comment (CUDA Toolkit is now resolved lazily)
* Studio: retrigger Windows GGUF CI (artifact upload flake)
