feat: add server process cleanup before exit in CosmicJarsFrame

Ensure the Minecraft server process is properly destroyed before exiting
the application. This prevents potential orphaned processes when the
application is closed.

Author: GeorgeV220

src/main/java/com/georgev22/cosmicjars/CosmicJarsFrame.java

@@ -48,7 +48,13 @@ public CosmicJarsFrame() {
         JMenu helpMenu = new JMenu("Help");
 
         JMenuItem exitItem = new JMenuItem("Exit");
-        exitItem.addActionListener(e -> System.exit(0));
+        exitItem.addActionListener(e -> {
+            MinecraftServer server = main.getMinecraftServer();
+            if (server != null && (server.getMinecraftServerProcess() != null && server.getMinecraftServerProcess().isAlive())) {
+                server.getMinecraftServerProcess().destroy();
+            }
+            System.exit(0);
+        });
         fileMenu.add(exitItem);
         JMenuItem configItem = new JMenuItem("Config");
         configItem.addActionListener(e -> ConfigPopup.showConfigPopup());