release: RememberStack 0.6.0

[fazpu]

Problem

v0.5.0 ends at the PostgreSQL 19 cut and does not publish the D97 default retrieval implementation merged in #316. Consumers need one installable version boundary for that completed identity and retrieval slice.

Scope

• bump the shared PyPI, GHCR, and Compose coordinate to 0.6.0
• update the README and public docs to point at v0.6.0
• document the default fact_context composition, assured-operation v2, saved-query upgrade, and PostgreSQL planner/readiness safeguards

Important decision

This is a minor release because #316 adds a public retrieval capability and versions its operation contract; it is not a patch-only correction.

Sources inspected

• release contract and workflow: scripts/check_release_contract.py, .github/workflows/release.yml
• prior release cut: release: RememberStack 0.4.3 #306
• release boundary: v0.5.0 is 050f9f61; feat(retrieval): compose D97 default fact context #316 is the only first-parent commit after it

Validation

• uv run python scripts/check_release_contract.py --tag v0.6.0
• uv lock --check
• uv build and wheel metadata inspection
• uv run pytest src/tests/packaging/test_release_contract.py -q
• docker compose config --quiet
• pnpm --dir website run build
• git diff --check

Limitations and follow-up

This PR only cuts the version and release documentation. The tag-triggered workflow remains responsible for the full release suite and publication to PyPI, GHCR, and GitHub Releases after merge.

Contributor agreement

Signing on behalf of a legal entity (leave blank if accepting individually):

• I have read and agree to the RememberStack Contributor License Agreement v1.0.