feat(channel-monitor): gate UI by feature switch + polish form UX

- AppSidebar 三处菜单项（管理端渠道监控、用户端/个人页渠道状态）按
  channel_monitor_enabled 条件展开，关闭时隐藏
- ChannelStatusView setInterval 随开关启停：关闭 clearInterval，
  开启/未知态自动启动，避免禁用功能后仍在轮询
- MonitorFormDialog provider Select 改为 3 色单选按钮
  （openai=emerald / anthropic=orange / gemini=sky），i18n 文案
  供应商 → 平台 / Provider → Platform
- MonitorKeyPickerDialog 按钮列表改为 name/key/group 三列表格 +
  搜索框，按 key.group.platform === provider 过滤，避免跨平台误选
- form.provider 变化时清空 api_key，修复切换平台仍保留旧 key 的
  错配 bug
- providerPickerClass 抽取到 useChannelMonitorFormat composable，
  统一 emerald/orange/sky 颜色语义，消除硬编码 Tailwind class 重复
- maskApiKey 工具函数统一（utils/maskApiKey.ts），KeysView 与
  MonitorKeyPickerDialog 共用 slice(0,6)...slice(-4) 策略
- bump version to 0.1.114.27

frontend/src/components/layout/AppSidebar.vue

@@ -611,7 +611,9 @@ const userNavItems = computed((): NavItem[] => {
     { path: '/dashboard', label: t('nav.dashboard'), icon: DashboardIcon },
     { path: '/keys', label: t('nav.apiKeys'), icon: KeyIcon },
     { path: '/usage', label: t('nav.usage'), icon: ChartIcon, hideInSimpleMode: true },
-    { path: '/monitor', label: t('nav.channelStatus'), icon: SignalIcon },
+    ...(appStore.cachedPublicSettings?.channel_monitor_enabled
+      ? [{ path: '/monitor', label: t('nav.channelStatus'), icon: SignalIcon }]
+      : []),
     { path: '/subscriptions', label: t('nav.mySubscriptions'), icon: CreditCardIcon, hideInSimpleMode: true },
     ...(appStore.cachedPublicSettings?.payment_enabled
       ? [
@@ -650,7 +652,9 @@ const personalNavItems = computed((): NavItem[] => {
   const items: NavItem[] = [
     { path: '/keys', label: t('nav.apiKeys'), icon: KeyIcon },
     { path: '/usage', label: t('nav.usage'), icon: ChartIcon, hideInSimpleMode: true },
-    { path: '/monitor', label: t('nav.channelStatus'), icon: SignalIcon },
+    ...(appStore.cachedPublicSettings?.channel_monitor_enabled
+      ? [{ path: '/monitor', label: t('nav.channelStatus'), icon: SignalIcon }]
+      : []),
     { path: '/subscriptions', label: t('nav.mySubscriptions'), icon: CreditCardIcon, hideInSimpleMode: true },
     ...(appStore.cachedPublicSettings?.payment_enabled
       ? [
@@ -715,7 +719,9 @@ const adminNavItems = computed((): NavItem[] => {
       expandOnly: true,
       children: [
         { path: '/admin/channels/pricing', label: t('nav.channelPricing'), icon: PriceTagIcon },
-        { path: '/admin/channels/monitor', label: t('nav.channelMonitor'), icon: SignalIcon },
+        ...(appStore.cachedPublicSettings?.channel_monitor_enabled
+          ? [{ path: '/admin/channels/monitor', label: t('nav.channelMonitor'), icon: SignalIcon }]
+          : []),
       ],
     },
     { path: '/admin/subscriptions', label: t('nav.subscriptions'), icon: CreditCardIcon, hideInSimpleMode: true },