TASK-083: persist 39 unworked review findings

8 major (bench stat-helper DRY consolidation into bench_harness.hpp) and
31 minor findings deferred from the iteration-1 review pass, recorded for
a later cleanup sweep.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Rkuh4aSmrD8m2f2vYqakb6

Author: etr