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/composables/useChannelMonitorFormat.ts

@@ -76,6 +76,32 @@ export function useChannelMonitorFormat() {
     }
   }
 
+  /**
+   * Tailwind class for a provider radio-button-style picker (active/inactive state).
+   * Reuses the same emerald/orange/sky palette as providerBadgeClass to keep
+   * visual semantics consistent across badges and pickers.
+   */
+  function providerPickerClass(p: Provider | string, active: boolean): string {
+    switch (p) {
+      case PROVIDER_OPENAI:
+        return active
+          ? 'border-emerald-500 bg-emerald-50 text-emerald-700 dark:bg-emerald-500/15 dark:text-emerald-300 dark:border-emerald-400'
+          : 'border-gray-200 bg-white text-gray-600 hover:border-emerald-300 hover:text-emerald-700 dark:border-dark-700 dark:bg-dark-800 dark:text-gray-400 dark:hover:border-emerald-500/50'
+      case PROVIDER_ANTHROPIC:
+        return active
+          ? 'border-orange-500 bg-orange-50 text-orange-700 dark:bg-orange-500/15 dark:text-orange-300 dark:border-orange-400'
+          : 'border-gray-200 bg-white text-gray-600 hover:border-orange-300 hover:text-orange-700 dark:border-dark-700 dark:bg-dark-800 dark:text-gray-400 dark:hover:border-orange-500/50'
+      case PROVIDER_GEMINI:
+        return active
+          ? 'border-sky-500 bg-sky-50 text-sky-700 dark:bg-sky-500/15 dark:text-sky-300 dark:border-sky-400'
+          : 'border-gray-200 bg-white text-gray-600 hover:border-sky-300 hover:text-sky-700 dark:border-dark-700 dark:bg-dark-800 dark:text-gray-400 dark:hover:border-sky-500/50'
+      default:
+        return active
+          ? 'border-gray-400 bg-gray-50 text-gray-700 dark:border-dark-500 dark:bg-dark-700 dark:text-gray-200'
+          : 'border-gray-200 bg-white text-gray-600 hover:border-gray-300 dark:border-dark-700 dark:bg-dark-800 dark:text-gray-400'
+    }
+  }
+
   function formatLatency(ms: number | null | undefined): string {
     if (ms == null) return t('monitorCommon.latencyEmpty')
     return String(Math.round(ms))
@@ -110,6 +136,7 @@ export function useChannelMonitorFormat() {
     statusBadgeClass,
     providerLabel,
     providerBadgeClass,
+    providerPickerClass,
     formatLatency,
     formatPercent,
     formatAvailability,