chore: Update documentation and improve test writing guidelines

modules/core/src/main/scala/de/nowchess/chess/Main.scala

@@ -3,6 +3,8 @@ package de.nowchess.chess
 import de.nowchess.api.board.{Board, Color}
 import de.nowchess.chess.controller.GameController
 
-@main def chessMain(): Unit =
-  println("NowChess TUI — type moves in coordinate notation (e.g. e2e4). Type 'quit' to exit.")
-  GameController.gameLoop(Board.initial, Color.White)
+object Main {
+  def main(args: Array[String]): Unit =
+    println("NowChess TUI — type moves in coordinate notation (e.g. e2e4). Type 'quit' to exit.")
+    GameController.gameLoop(Board.initial, Color.White)
+}