CI: record Windows build and test failures (baseline)

[basal-alfonso]

Adds a non-blocking windows-latest job that runs cargo check and cargo test across the workspace and uploads the full failure list. It's a draft that measures what Windows needs before the Windows build work starts, and isn't meant to merge as is.

---

Summary by cubic

Adds a non-blocking windows-latest CI job that runs cargo check and cargo test across the workspace and records the full failure list, so Windows support work can start from measured failures instead of guesses. The job continues on error, never fails the workflow, and uploads all logs as the windows-baseline-logs artifact. This is a draft baseline and isn't meant to merge as is.

^{Written for commit 8bb6e31. Summary will update on new commits.}

[basal-alfonso]

Superseded: the baseline job is now on main (a7655a9), with the measured failure list in evidence/windows-build-failures.md.