release: prepare base-bash-libs 2.2.0

[codeforester]

Summary

• advance VERSION and embedded release metadata to 2.2.0;
• move the reviewed Unreleased entries into the dated 2026-10-07 changelog section;
• update the top README release row and canonical asset links;
• make the release-invariants additive-candidate fixture derive a version newer than the candidate, so release preparation remains testable at 2.2.0.

Validation

• git diff --check
• bash tests/changelog-guard.sh
• bash tests/docs-contract.sh
• scripts/release-artifact build/verify against the clean preparation commit
• ./tests/validate.sh: 712 tests and all release, artifact, property, integration, quality, and CI-policy stages passed

Release safety

No tag or GitHub Release is published by this PR. Publication will use the merged commit only after hosted checks pass, followed by verify-remote. The base-bash-libs-demo v0.1.0 update remains explicitly deferred to demo #38 until v2.2.0 is immutable.

Fixes #564