feat: add PGN exporter for game notation

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

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

@@ -46,6 +46,7 @@ class PgnExporterTest extends AnyFunSuite with Matchers:
     pgn.contains("1. e2e4 c7c5") shouldBe true
     pgn.contains("2. g1f3") shouldBe true
   }
+<<<<<<< HEAD
 
   test("export game with no headers returns only move text") {
     val history = GameHistory()
@@ -63,3 +64,5 @@ class PgnExporterTest extends AnyFunSuite with Matchers:
 
     pgn.contains("O-O-O") shouldBe true
   }
+=======
+>>>>>>> 58a962c (feat: add PGN exporter for game notation)