feat: 加slsBoardEnabled规则作榜单总开关（服务端规则控制客户端命令）

BoardTogglePayload同步开关状态；客户端/slsboard检查enabled，未开启则拒绝。ServerMain加轮询线程检测规则变化。

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

@@ -80,4 +80,7 @@ public class SLSCarpetSettings {
 
     @Rule(categories = {SLSA, RuleCategory.FEATURE})
     public static boolean stackableVehicles = false;
+
+    @Rule(categories = {SLSA, RuleCategory.FEATURE})
+    public static boolean slsBoardEnabled = false;
 }