Post-V1: document release workflow with GitHub CLI #5

Document the release workflow used for v1.0.0 so future releases are reproducible.\n\nScope:\n- Include prerelease and stable release steps.\n- Include release gate, fresh-install smoke, demo drift, health checks, tag push, and gh release create.\n- Note that final publication still requires an explicit human go.\n- Link to RELEASE-V1.md where appropriate.