#4 Optimize review: small-PR and incremental fast paths

Summary

• Small PRs (<10 lines): single Opus call instead of full 3-member council (1 invocation vs 4)
• Re-reviews (prior marker exists): single Opus call with prior review context, focused on delta
• First review of non-small PRs: full council (unchanged)
• New config: SMALL_PR_THRESHOLD repo variable (default 10)

Cost impact

• Small docs PRs (like .github#101): ~1 min instead of ~5 min, 1 invocation instead of 4
• Re-reviews after Claude fixes: ~1 min focused check instead of full re-analysis
• Full council: unchanged for substantive first reviews

Test plan

• Let the automation review and merge this PR
• Verify mode detection in logs (mode: small|incremental|full)
• Verify small PR uses single Opus path
• Verify re-review after new commits uses incremental path

🤖 Generated with Claude Code