Drop variant B, adopt Black-belt Exam defender, add one-sidedness metrics

- Remove variant B (Brown cap, +1 for higher beating lower) from rules,
  engine, bots and simulator; a higher belt beating a lower one gains 0.
- Final Exam: the defender fights as a Black belt (RULES.md v0.7). Ties to
  the defender and best-of-3 stay as simulator switches (`--exam`).
- Report stripe income per source as gains and losses.
- Add ten one-sidedness measures sampled at turn ends (lead gap, winner
  margin and lead share, halfway leader, last lead change, contention,
  rank swaps, leader Kumite losses, Exam challengers, winner pace).
- Plan: decisions D28-D33 and the detailed Phase 6.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

README.md

@@ -39,11 +39,12 @@ listed values is a scenario; game `i` of each scenario uses seed `--seed + i`, a
 rotates one seat per game. Bots: `random`, `balanced`, `farmer`, `aggressive`.
 
 ```sh
-uv run dojo sim                                   # variants A and B, 4 players, 200 games each
+uv run dojo sim                                   # 4 players, current rules, 200 games
 uv run dojo sim --games 1000 --csv games.csv      # more games; one CSV row per game
-uv run dojo sim --variant B --players 3 4 6 8 --start 0 3   # player counts x start position
+uv run dojo sim --exam c none a ac                # Final Exam options in force (rules: c), combinable
+uv run dojo sim --players 3 4 6 8 --start 0 3     # player counts x start position
 uv run dojo sim --kiai 2 1                        # Kiai +2 vs +1
-uv run dojo sim --lineup balanced,random balanced # several lineups (comma-separated seats)
+uv run dojo sim --lineup farmer aggressive,farmer # several lineups (comma-separated seats)
 uv run dojo sim --seed 42 --jobs 1                # other dice; single process
 ```