Document Windows parity contract and operator workflow

[muscariello]

• Target files:
  • .github/workflows/* (or equivalent CI config)
• Problem:
  • Windows parity cannot be trusted long-term without sustained CI validation.
• Scope:
  • Add/expand Windows integration job with artifacts/logs.
  • Start as non-blocking, then promote to required after stability window.
• Acceptance criteria:
  • Windows integration workflow exists and is reproducible.
  • Failure logs are sufficient for diagnosis.
  • Rollout plan documented in PR.