release: prepare base-bash-libs 2.2.1

[codeforester]

Summary

• prepare the base-bash-libs v2.2.1 patch release
• align release metadata, changelog, README, quickstart, versioning, pinned-consumption, and validation documentation
• keep the release artifact metadata placeholders intact for final merged-commit publication
• make the documentation contract verify immutable tag resolution rather than a self-referential commit pin

This is a documentation and release-contract patch; no public API or runtime behavior changes are intended.

Issue

Fixes #571

Validation

• git diff --check
• bash tests/docs-contract.sh
• bash tests/changelog-guard.sh
• env BASE_CACHE_DIR=/private/tmp/base-release-221-check scripts/release check --version 2.2.1 --manifest base_manifest.yaml
• ./tests/validate.sh (712 BATS cases plus Bash, artifact, property, quality, CI-policy, and release-invariant gates)

Release safety

The final archive, SBOM, provenance, checksum manifest, and annotated tag must be built from the merged main commit after this PR is merged. No existing tag or asset is rewritten.