Villager Chess

First public release.

Added

• Play Chess button on every villager's trade screen - challenge any villager to a full game of chess (you play White).
• Difficulty scales with the villager's trading level: Novice (hangs pieces) → Apprentice → Journeyman → Expert → Master (near-unbeatable).
• Full chess rules: castling, en passant, pawn promotion with a piece picker, threefold repetition, 50-move rule, and insufficient-material draws.
• Click-to-move board UI with legal-move highlights, check indicator, and Resign/Close buttons.
• Abandon handling: walking more than 16 blocks away, the villager dying, or disconnecting abandons the game; closing the board resigns.
• From-scratch chess engine (negamax + alpha-beta + iterative deepening + quiescence search) running on a background thread; move generation is perft-verified.
• Fully server-authoritative: the server owns all game state; clients only send move attempts.

Fixed

• The Play Chess button now stacks below other Villager Games mods' trade-screen buttons instead of landing on the same pixel. With only this mod installed the button is exactly where it was.