Remove prerelease release-recovery machinery

[rmcdaniel]

Summary

• remove the retired scheduled release-plan recovery workflow and copied recovery engine
• remove prerelease recovery conformance from ordinary package CI
• keep direct immutable-tag PyPI publishing, artifact validation, package smoke tests, and release docs deployment

Tracks durable-workflow/.github#115.

Verification

• 1,381 unit tests passed; 2 skipped; integration tests excluded locally
• Ruff and strict mypy passed
• wheel and sdist built, passed twine check, matched source release metadata, and passed installed-package smoke tests
• Actions workflows passed actionlint
• public-boundary and diff checks passed