fix: 修复objective重复创建崩溃（ensure推迟到scoreboard load后）

onServerLoaded时机太早，scoreboard.dat还没load完，getObjective返回null导致重复addObjective崩溃。改为syncScores首次调用时ensure。

src/main/java/com/github/zly2006/carpetslsaddition/ServerMain.java

@@ -54,7 +54,6 @@ public class ServerMain implements ModInitializer, CarpetExtension {
     public void onServerLoaded(MinecraftServer server) {
         ServerMain.server = server;
         com.github.zly2006.carpetslsaddition.util.BotListManager.load();
-        com.github.zly2006.carpetslsaddition.util.BoardManager.ensureObjectives(server);
         startBoardWatcher(server);
     }