GitLab

The public settings API filters out menu items with visibility='admin',
so customMenuItemsForAdmin was always empty when reading from
cachedPublicSettings. Fix by loading custom menu items from the admin
settings API (via adminSettingsStore) which returns all items unfiltered.

Changes:
- adminSettings store: store custom_menu_items from admin settings API
- AppSidebar: read admin menu items from adminSettingsStore instead of
  cachedPublicSettings
- CustomPageView: merge public and admin menu items so admin users can
  access admin-only custom pages

- 新增 adminSettings store 管理 ops 配置状态
- 注册 adminSettings store 到全局 store
- 添加 ops 监控相关路由（dashboard, alerts, realtime, settings）