feat: leaderboard

Add LeaderboardManager class to handle score submission and retrieval. Integrate leaderboard display into the main menu UI. Sync player scores with the local save system.

Author: huynhtuan372

src/main/java/com/github/codestorm/bounceverse/Bounceverse.java

@@ -1,16 +1,20 @@
 package com.github.codestorm.bounceverse;
 
+import java.io.IOException;
+import java.util.Map;
+
 import com.almasb.fxgl.app.GameApplication;
 import com.almasb.fxgl.app.GameSettings;
-import com.github.codestorm.bounceverse.systems.init.*;
+import com.github.codestorm.bounceverse.systems.init.AppEventSystem;
+import com.github.codestorm.bounceverse.systems.init.GameSystem;
+import com.github.codestorm.bounceverse.systems.init.InputSystem;
+import com.github.codestorm.bounceverse.systems.init.PhysicSystem;
+import com.github.codestorm.bounceverse.systems.init.UISystem;
 import com.github.codestorm.bounceverse.systems.manager.settings.GameSettingsManager;
 import com.github.codestorm.bounceverse.systems.manager.settings.LaunchOptionsManager;
 import com.github.codestorm.bounceverse.systems.manager.settings.UserSettingsManager;
 import com.github.codestorm.bounceverse.typing.exceptions.BounceverseException;
 
-import java.io.IOException;
-import java.util.Map;
-
 /**
  *
  *