refactor(core): cleanup UI and notation imports for NCS-22 interface abstraction

- Removed unused CastleSide import from PgnExporter
- Updated TerminalUI and GUIObserver to use GameContext
- Temporarily disabled GUI FEN/PGN import-export (requires full rework with GameContext)
- Deleted unused logic files and GameController per spec

Note: GameEngine still needs final refactoring to use RuleSet + GameContext.
Core architecture (api -> rule -> core) is structurally complete.

modules/core/src/main/scala/de/nowchess/chess/notation/PgnExporter.scala

@@ -3,7 +3,6 @@ package de.nowchess.chess.notation
 import de.nowchess.api.board.{PieceType, *}
 import de.nowchess.api.move.PromotionPiece
 import de.nowchess.api.game.{GameHistory, HistoryMove}
-import de.nowchess.chess.logic.CastleSide
 
 object PgnExporter:
 

modules/core/src/main/scala/de/nowchess/chess/notation/PgnParser.scala

@@ -3,7 +3,6 @@ package de.nowchess.chess.notation
 import de.nowchess.api.board.*
 import de.nowchess.api.move.PromotionPiece
 import de.nowchess.api.game.{GameHistory, HistoryMove}
-import de.nowchess.chess.logic.{CastleSide, GameRules, MoveValidator, withCastle}
 
 /** A parsed PGN game containing headers and the resolved move list. */
 case class PgnGame(