feat: NCS-11 derive PGN termination marker from Result header

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

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

@@ -22,7 +22,8 @@ object PgnExporter:
         if blackMoveStr.isEmpty then s"$moveNum. $whiteMoveStr"
         else s"$moveNum. $whiteMoveStr $blackMoveStr"
 
-      moveLines.mkString(" ") + " *"
+      val termination = headers.getOrElse("Result", "*")
+      moveLines.mkString(" ") + s" $termination"
 
     if headerLines.isEmpty then moveText
     else if moveText.isEmpty then headerLines

modules/core/src/test/scala/de/nowchess/chess/notation/PgnExporterTest.scala

@@ -100,3 +100,15 @@ class PgnExporterTest extends AnyFunSuite with Matchers:
     pgn should include ("e2e4")
     pgn should not include ("=")
   }
+
+  test("exportGame uses Result header as termination marker"):
+    val history = GameHistory()
+      .addMove(HistoryMove(Square(File.E, Rank.R2), Square(File.E, Rank.R4), None))
+    val pgn = PgnExporter.exportGame(Map("Result" -> "1/2-1/2"), history)
+    pgn should endWith("1/2-1/2")
+
+  test("exportGame with no Result header still uses * as default"):
+    val history = GameHistory()
+      .addMove(HistoryMove(Square(File.E, Rank.R2), Square(File.E, Rank.R4), None))
+    val pgn = PgnExporter.exportGame(Map.empty, history)
+    pgn shouldBe "1. e2e4 *"