Rank farming guards

This update keeps high-rank leaderboard progress tied to meaningful wins instead of volume farming.

Changes:

• Champion tanks no longer gain rank score when they beat non-Champion tanks.
• For every rank tier, once a tank has beaten the same opponent 50 straight times within 24 hours, additional wins over that opponent do not add rank score until the streak window breaks.

Recorded matches still count as battle records and still affect ordinary win/loss history. These rules only suppress the winner's rank-score gain in the farming cases above.