Remove prerelease release-recovery machinery

[rmcdaniel]

Summary

• remove the retired scheduled release-plan publisher and copied recovery engine
• remove the prerelease-only PHP/Waterline train guard and release recovery CI category
• keep direct stable package identity checks, framework and service-mode published smokes, docs deployment, and privileged workflow boundary tests
• run the remaining workflow boundary tests once in the qualification route instead of duplicating them

Tracks durable-workflow/.github#115.

Verification

• 434 PHPUnit tests passed; 1 skipped
• PHPStan passed
• Composer validation, Avro benchmark guard, and dependency-boundary checks passed on PHP 8.3
• CI routing and privileged workflow contract suites passed
• Actions workflows passed actionlint
• public-boundary and diff checks passed