test(core): add GameEngineLoadGameTest for loadGame/exportGame

Add 3 focused tests for GameEngine load/export functionality:
- loadGame with PgnParser validates PGN parsing and undo/redo state
- loadGame with FenParser validates position loading without move replay
- exportGame with PgnExporter validates PGN output

Fix: PgnParser now extends GameContextImport trait for consistency with FenParser.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

modules/core/src/test/scala/de/nowchess/chess/engine/GameEngineLoadGameTest.scala

@@ -0,0 +1,43 @@
+package de.nowchess.chess.engine
+
+import scala.collection.mutable
+import de.nowchess.api.board.{Board, Color}
+import de.nowchess.api.game.GameContext
+import de.nowchess.chess.observer.{Observer, GameEvent, PgnLoadedEvent}
+import de.nowchess.io.pgn.PgnParser
+import de.nowchess.io.fen.FenParser
+import de.nowchess.io.pgn.PgnExporter
+import de.nowchess.io.fen.FenExporter
+import org.scalatest.funsuite.AnyFunSuite
+import org.scalatest.matchers.should.Matchers
+
+class GameEngineLoadGameTest extends AnyFunSuite with Matchers:
+
+  test("loadGame with PgnParser: loads valid PGN and enables undo/redo"):
+    val engine = new GameEngine()
+    val pgn = "[Event \"Test\"]\n\n1. e4 e5\n"
+    val result = engine.loadGame(PgnParser, pgn)
+    result shouldBe Right(())
+    engine.context.moves.size shouldBe 2
+    engine.canUndo shouldBe true
+
+  test("loadGame with FenParser: loads position without replaying moves"):
+    val engine = new GameEngine()
+    val fen = "8/4P3/4k3/8/8/8/8/8 w - - 0 1"
+    val result = engine.loadGame(FenParser, fen)
+    result shouldBe Right(())
+    engine.context.moves.isEmpty shouldBe true
+    engine.canUndo shouldBe false
+
+  test("exportGame with PgnExporter: exports current game as PGN"):
+    val engine = new GameEngine()
+    engine.processUserInput("e2e4")
+    engine.processUserInput("e7e5")
+    val pgn = engine.exportGame(PgnExporter)
+    pgn.contains("e4") shouldBe true
+    pgn.contains("e5") shouldBe true
+
+  private class MockObserver extends Observer:
+    val events = mutable.ListBuffer[GameEvent]()
+    override def onGameEvent(event: GameEvent): Unit =
+      events += event

modules/io/src/main/scala/de/nowchess/io/pgn/PgnParser.scala

@@ -3,6 +3,7 @@ package de.nowchess.io.pgn
 import de.nowchess.api.board.*
 import de.nowchess.api.move.{Move, MoveType, PromotionPiece}
 import de.nowchess.api.game.{GameContext, HistoryMove}
+import de.nowchess.io.GameContextImport
 import de.nowchess.rules.sets.DefaultRules
 
 /** A parsed PGN game containing headers and the resolved move list. */
@@ -11,7 +12,7 @@ case class PgnGame(
   moves: List[HistoryMove]
 )
 
-object PgnParser:
+object PgnParser extends GameContextImport:
 
   /** Strictly validate a PGN text.
    *  Returns Right(PgnGame) if every move token is a legal move in the evolving position.