Run optional plan-indexed review validation #19

The paired human review experiment prepared under PR #18 was cancelled by product decision before any timed results were recorded. The cancellation removes the experiment as a blocker for subsequent Codeboost roadmap work; it does not validate plan-indexed review speed or catch rate.

Run a future validation only when reviewer time and representative review work are available. Before starting:

• choose fresh packages and preserve reviewer blindness;
• commit the protocol, ordering, thresholds, and exact revisions before timing;
• keep automated review off experimental drafts until human decisions are recorded; and
• record decisions before unblinding or calculating results.

This issue is non-blocking. Product and implementation work may proceed without it, but documentation and product claims must not state that the cancelled gate passed.