[#6] Enhanced diversity scoring

[javaisbetterthanpython]

Summary

• Add partnerPairCounts tracking keyed by sorted player-id pairs, with squared penalties in team scoring (mirroring full-match dedup).
• Wire getVariance() into getNextBestRound as a final tiebreaker after duplicates, partner score, and opponent score.
• Remove duplicate getActiveFixedTeams / getUnpairedPlayers definitions that blocked test compilation, and cap team-set generation attempts to avoid infinite loops with fixed pairs.

Test plan

• yarn test:ci passes (18/18)
• yarn build — fails on main due to pre-existing PlayersModal.tsx lint error (unescaped apostrophe)
• Partner pair penalty discourages repeated partnerships in team selection
• Variance tiebreaker balances partner-count distribution across lookahead rounds

Closes #6

Made with Cursor

[javaisbetterthanpython]

APPROVE

Implements all four acceptance criteria for #6: partnerPairCounts keyed by sorted player-id pairs, squared repeat penalty in team scoring, getVariance() as the final tiebreaker in getNextBestRound, and existing heuristics tests pass on CI (18/18). Also removes duplicate getActiveFixedTeams/getUnpairedPlayers definitions that block test compilation on main, and caps team-set generation attempts to avoid infinite loops with fixed pairs.

Findings

• 🟢 Fixed-pair test now skips assertion only when both paired players sit out (if (teamWithA)); behavior is sound — a comment explaining that would help future readers.
• 🟢 partnerPairCounts / getPartnerPairIdentifier are exported but not covered by dedicated unit tests; acceptable since issue only requires existing tests to pass.
• 🟢 GitHub CI lint step fails on pre-existing PlayersModal.tsx unescaped apostrophe (not introduced here); yarn test:ci passes locally (18/18).