Wire the Tier-3 quarantined integration-test CI job once real tests exist

## Problem / goal

Wire the Tier-3 quarantined real-window integration-test CI job, once a real Tier-3 test exists to run. Not scheduled to a specific roadmap milestone — it's triggered by a precondition (the first such test landing), not a roadmap phase.

## References

- `docs/engineering/testing.md` §2 (Tier 3 traits, `continue-on-error: true` job requirement) and §7 (CI runner realities enabling Tier 3 on `windows-latest`).
- `.github/workflows/ci.yml`'s own trailing comment block, which explains exactly why this job isn't wired yet: Microsoft.Testing.Platform's zero-discovered-tests hard failure (`docs/engineering/testing.md` §1/§2) — wiring a filtered job against zero matching tests fails for the wrong reason (looks like a real CI break, is actually "nothing to run yet").
- Depends on the Bastion.TestWindows-extension issue (v0.1) and, more directly, on whoever writes the first actual `[Trait("Category","Quarantined")]` test class consuming it (not yet filed as its own issue, since it's naturally part of whichever v0.1 issue's implementer decides to add a real-window integration test first).

## Acceptance criteria

- [ ] At least one test carries `[Trait("Category", "Quarantined")]`.
- [ ] A `.github/workflows/ci.yml` job runs `dotnet test --filter-query "/[Category=Quarantined]"` on `windows-latest` with `continue-on-error: true`.
- [ ] The job's failures are visibly separated from the main gate in PR checks (clearly labeled, e.g. in the job's `name:`) so a red Tier 3 job is never mistaken for a blocking failure.

Start with docs/engineering/testing.md sections 1, 2, and 7, then read the trailing comment block in .github/workflows/ci.yml. After a real [Trait("Category", "Quarantined")] test exists, run the filtered test locally on Windows and wire the windows-latest job in ci.yml. Done means the job is clearly labeled, uses the specified filter, continues on error, and is separate from the main gate.

Written by the indexing model from the issue text.