koala-artifact 1.0.4

Reviewer artifact format and sampling verifier.
Documentation

Reviewer artifact record / verify.

Stage 4 implementation of ADR-0003 (artifact-over-signing) and ADR-0005 (sampling verification). Reviewers record a command and its output into .review/round-N/<kind>-<name>.md; CI later verifys a sample by re-running each command and comparing the normalised hash.