Two bugs in move notation causing PGN import failures in LiChess:
1. Disambiguation: when two pieces of same type can reach same square,
SAN requires file/rank/full-square prefix (e.g. "Ndf3" not "Nf3").
Added disambiguate() in PgnExporter and disambiguatePiece() in
GameEngine, both querying allLegalMoves to find competing pieces.
2. Check/checkmate suffix: "+" and "#" were never appended.
PgnExporter now threads ctxAfter through moveToAlgebraic and
calls DefaultRules.isCheck/isCheckmate. GameEngine passes
PostMoveStatus to translateMoveToNotation for the same result.
Also removes dead notation code in executeMoveBody (result was never
used — not passed to MoveExecutedEvent).
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Janis Eccarius