feat: complete PostgreSQL runtime contract

[joey-huckabee]

Summary

• harden initialization, SCRAM authentication, immutable configuration, logging, and mounted TLS behavior
• qualify durable storage, crash recovery, resource exhaustion, logical backup/restore, and PostgreSQL 18 minor updates on native AMD64 and ARM64
• publish detailed deployment and operations playbooks for the planned v1 profiles
• record Package 3 completion and preserve the unreleased support boundary

Validation

• pre-commit run --all-files --show-diff-on-failure
• native AMD64 and ARM64 CI: https://github.com/datopsis/postgresql-ubi/actions/runs/34647961464
• final documentation revision CI: https://github.com/datopsis/postgresql-ubi/actions/runs/34648401019