refactor: NCS-19 Currying (#18)

Summary

  - Curried candidateMoves, legalMoves, and applyMove in the RuleSet trait to separate (context) as the world being
  operated on from the computation parameter
  - Updated DefaultRules overrides and all internal call sites
  - Updated all external call sites: GameEngine, PgnParser, PgnExporter, ChessBoardView, and all affected tests

  Test plan

  - All existing tests pass (./gradlew build)
  - No behaviour changes — pure style refactoring, existing test suite is the regression guard

Co-authored-by: LQ63 <lkhermann@web.de>
Reviewed-on: #18
Reviewed-by: Janis <janis-e@gmx.de>
Co-authored-by: Leon Hermann <lq@blackhole.local>
Co-committed-by: Leon Hermann <lq@blackhole.local>

modules/ui/src/main/scala/de/nowchess/ui/gui/ChessBoardView.scala

@@ -178,7 +178,7 @@ class ChessBoardView(val stage: Stage, private val engine: GameEngine) extends B
             selectedSquare = Some(clickedSquare)
             highlightSquare(rank, file, PieceSprites.SquareColors.Selected)
 
-            val legalDests = engine.ruleSet.legalMoves(engine.context, clickedSquare)
+            val legalDests = engine.ruleSet.legalMoves(engine.context)(clickedSquare)
                .collect { case move if move.from == clickedSquare => move.to }
             legalDests.foreach { sq =>
                highlightSquare(sq.rank.ordinal, sq.file.ordinal, PieceSprites.SquareColors.ValidMove)