chore: prepare v1.12.0 release

[davidahmann]

Release prep

Finalize the changelog-derived v1.12.0 minor release from v1.11.2 and keep public install, action, UAT, and freeze-receipt contracts aligned with the finalized release section.

Changes

• promote all releasable Unreleased entries into the dated v1.12.0 changelog section through the Factory finalizer
• reset Unreleased sections for the next development cycle
• pin existing README, docs, Action, and UAT examples to v1.12.0
• refresh the source-bound Sprint 0 freeze receipt digest for the release-version README change

Validation

• python3 factory/scripts/resolve_release_version.py --repo-root . --json
• python3 factory/scripts/finalize_release_changelog.py --repo-root . --release-version v1.12.0 --json
• python3 factory/scripts/validate_release_changelog.py --repo-root . --release-version v1.12.0 --json
• go test ./testinfra/hygiene -run 'TestInstallDocsPinnedVersionSupportsCurrentReadmeCommands|TestMinimalDependenciesReleaseSmokeVersionIsCurrent' -count=1
• make test-docs-consistency
• make test-freeze-gate
• make prepush-full

Risk

Release metadata and documentation only; no runtime implementation changes. Factory remains unchanged and clean at the repository-pinned commit.