Remove prerelease release-recovery machinery

[rmcdaniel]

Summary

• remove the retired scheduled release-plan recovery workflow and copied recovery engine
• remove prerelease plan-tag publication and recovery conformance from ordinary CI
• keep direct exact-tag crates.io publication, GitHub Release creation, crate identity verification, and release-tool tests
• simplify the direct release input surface to the immutable tag and commit it actually uses

Tracks durable-workflow/.github#115.

Verification

• Rust 1.86 formatting passed
• 199 library and integration tests passed across all targets
• cargo package built and recompiled the publishable crate
• release publication, package verification, crates.io maintenance, URL, and source-qualification test suites passed
• Actions workflows passed actionlint
• public-boundary and diff checks passed

Strict Clippy was also sampled as an advisory check and reported four pre-existing style lints outside this cleanup; the repository CI does not require Clippy.