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/resources/assets/slsaddition/lang/en_us.json

@@ -74,5 +74,7 @@
 
   "carpet.slsa.block.deep_slate_core": "Deepslate Core",
   "carpet.rule.stackableVehicles.name": "Stackable vehicles",
-  "carpet.rule.stackableVehicles.desc": "Minecarts and boats can stack up to 64, auto-merging on pickup"
+  "carpet.rule.stackableVehicles.desc": "Minecarts and boats can stack up to 64, auto-merging on pickup",
+  "carpet.rule.slsBoardEnabled.name": "Enable boards",
+  "carpet.rule.slsBoardEnabled.desc": "Allow players to use /slsboard to show death/mining leaderboards"
 }