Surface Prow OWNERS discovery, log revision SHAs, and add the Case Lab

[daichunghy]

Summary

Implements the decisions recorded in docs/reviews/2026-09-03-feedback-improvements.md:

1. Root OWNERS and OWNERS_ALIASES files are surfaced by discovery as needs_confirmation findings (authority: discovery_only, prow_owners signal). They cannot create a blocking requirement; the enforceable ownership contract (CODEOWNERS, explicit patchgate.yml, native GitHub controls) is unchanged.
2. The Action console output now logs Base SHA, Head SHA, Tested SHA, and Evidence Target alongside the existing digests (the check summary already shows them after the tested-SHA binding work).
3. Adds the replayable Case Lab doc and npm run case-lab alias, links it from the README, and records the 2026-09-03 feedback evidence (Falco Prow ownership model, Discussion A green check from the wrong commit is still the wrong evidence #29 SHA visibility, consumer-docs gate).

Verification

• npm run verify passes locally on the merged tree (lint, typecheck, fixtures, security, GitHub integration, bundle, consumer fixture, CLI smoke).

Maintainer decision merge; not independent-review evidence.