Retired engineering documents

Point-in-time audits, migration ledgers, and superseded implementation plans were removed from the current source tree during 2.3.1 cleanup. They are ordinary historical documentation, not current product contracts. Current guides are indexed in ../README.md.

The last pre-cleanup snapshot is commit ae5a4e231ff2f8f24eeb0abaded1df121cdcf7db. Use Git history to retrieve the former docs/archive/ documents. Release notes and benchmark-integrity ledgers remain in the repository because they carry public contracts.

Removing a file here does not remove earlier Git history, forks, or released artifacts. Confirmed secrets require revocation/rotation and a separately reviewed history-remediation process, not an archive directory or a link to the exposed value.