feat: 支持 RPC 节点启用/禁用功能

- 后端：更新 RpcNodeService，确保禁用的节点被忽略
  - getAllNodesWithDefault() 只返回启用的节点
  - checkAllNodesHealth() 只检查启用的节点
  - getAvailableNode() 已正确实现，只查询启用的节点

- 前端：添加启用/禁用开关功能
  - 在 RpcNodeSettings 页面添加启用列，使用 Switch 组件
  - 添加 handleToggleEnabled 函数处理启用/禁用切换
  - 添加多语言支持（中文简体、繁体、英文）

frontend/src/locales/en/common.json

@@ -1084,8 +1084,12 @@
     "statusUnhealthy": "Unavailable",
     "statusUnknown": "Unknown",
     "responseTime": "Response Time",
+    "enabled": "Enabled",
     "actions": "Actions",
     "check": "Check",
+    "enableSuccess": "Enabled successfully",
+    "disableSuccess": "Disabled successfully",
+    "updateFailed": "Update failed",
     "checkSuccess": "Check completed",
     "checkFailed": "Check failed",
     "deleteConfirm": "Are you sure you want to delete this node?",