Add references/agent-evals.md documenting the official supabase/evals
harness: eval/experiment concepts, the tools and local-stack runtimes,
run and result-viewing commands, and a mapping of harness scenarios to
the skill's operating references. Route to it from the supabase
"Choose the path" table and from postgres, agent-evals-and-observability,
backend-engineering, and data-engineering. Add two eval cases covering
the new reference and keep the generated catalog artifacts current.
Closes#271
Co-authored-by: factory-droid[bot] <138933559+factory-droid[bot]@users.noreply.github.com>