feat: Gui added (not done, not reviewed)

modules/ui/src/main/scala/de/nowchess/ui/Main.scala

@@ -2,14 +2,20 @@ package de.nowchess.ui
 
 import de.nowchess.chess.engine.GameEngine
 import de.nowchess.ui.terminal.TerminalUI
+import de.nowchess.gui.ChessGUILauncher
 
-/** Application entry point - starts the Terminal UI for the chess game. */
+/** Application entry point - starts both GUI and Terminal UI for the chess game.
+ *  Both views subscribe to the same GameEngine via Observer pattern.
+ */
 object Main:
   def main(args: Array[String]): Unit =
     // Create the core game engine (single source of truth)
     val engine = new GameEngine()
 
-    // Create and start the terminal UI
+    // Launch ScalaFX GUI in separate thread
+    ChessGUILauncher.launch(engine)
+
+    // Create and start the terminal UI (blocks on main thread)
     val tui = new TerminalUI(engine)
     tui.start()