feat(monitor): admin channel monitor MVP with SSRF protection and batch aggregation

新增 admin「渠道监控」模块（参考 BingZi-233/check-cx），独立于现有 Channel 体系。
admin 配置 + 后台定时调用上游 LLM chat completions 健康检查 + 所有登录用户只读可见。

后端：
- ent: channel_monitor + channel_monitor_history（AES-256-GCM 加密 api_key）
- service 按职责拆分：service/aggregator/validate/checker/runner/ssrf
- provider strategy map 替代 switch（openai/anthropic/gemini）
- repository batch 聚合（ListLatestForMonitorIDs + ComputeAvailabilityForMonitors）消除 N+1
- runner: ticker(5s) + pond worker pool(5) + inFlight 防并发 + TrySubmit 防雪崩
  + 凌晨 3 点 cron 清理 30 天历史
- SSRF 防护：强制 https + 私网/loopback/云元数据 IP 拒绝（127/8、10/8、172.16/12、
  192.168/16、169.254/16、100.64/10、::1、fc00::/7、fe80::/10）+ DialContext
  在 socket 层防 DNS rebinding
- API key sanitize：擦除 url.Error 与上游响应 body 中的 sk-/sk-ant-/AIza/JWT 模式
- APIKeyDecryptFailed 标志位 + 单 monitor 路径检测，避免空 key 调用上游

handler:
- admin: CRUD + 手动触发 + 历史接口（api_key 脱敏）
- user: 只读列表 + 状态详情（去除 api_key/endpoint）
- ParseChannelMonitorID 共用 + dto.ChannelMonitorExtraModelStatus 共用

前端：
- 路由 /admin/channels/{pricing,monitor} + /monitor（用户只读）
- AppSidebar 父项 expandOnly 支持
- ChannelMonitorView 拆为 8 个子组件 + ChannelStatusView 拆出 detail dialog
- composables/useChannelMonitorFormat + constants/channelMonitor 共享
- i18n monitorCommon namespace 消除 admin/user 两 view 重复

合规：所有文件符合 CLAUDE.md（Go ≤ 500 行 / Vue ≤ 300 行 / 函数 ≤ 30 行）
CI: go build / gofmt / golangci-lint(0 issues) / make test-unit / pnpm build 全绿

frontend/src/composables/useChannelMonitorFormat.ts

@@ -0,0 +1,97 @@
+/**
+ * Shared formatting helpers for channel monitor views (admin + user).
+ *
+ * Centralises:
+ *  - status / provider label + badge class lookups
+ *  - latency / availability / percent number formatting
+ *
+ * i18n keys live under `monitorCommon.*` so admin and user views share the
+ * same translation source.
+ */
+
+import { useI18n } from 'vue-i18n'
+import type { MonitorStatus, Provider } from '@/api/admin/channelMonitor'
+import {
+  PROVIDER_OPENAI,
+  PROVIDER_ANTHROPIC,
+  PROVIDER_GEMINI,
+  STATUS_OPERATIONAL,
+  STATUS_DEGRADED,
+  STATUS_FAILED,
+  STATUS_ERROR,
+} from '@/constants/channelMonitor'
+
+const NEUTRAL_BADGE = 'bg-gray-100 text-gray-800 dark:bg-dark-700 dark:text-gray-300'
+
+export interface AvailabilityRow {
+  primary_status: MonitorStatus | ''
+  availability_7d: number | null | undefined
+}
+
+export function useChannelMonitorFormat() {
+  const { t } = useI18n()
+
+  function statusLabel(s: MonitorStatus | ''): string {
+    if (!s) return t('monitorCommon.status.unknown')
+    return t(`monitorCommon.status.${s}`)
+  }
+
+  function statusBadgeClass(s: MonitorStatus | ''): string {
+    switch (s) {
+      case STATUS_OPERATIONAL:
+        return 'bg-green-100 text-green-800 dark:bg-green-900/30 dark:text-green-300'
+      case STATUS_DEGRADED:
+        return 'bg-yellow-100 text-yellow-800 dark:bg-yellow-900/30 dark:text-yellow-300'
+      case STATUS_FAILED:
+        return 'bg-red-100 text-red-800 dark:bg-red-900/30 dark:text-red-300'
+      case STATUS_ERROR:
+      default:
+        return NEUTRAL_BADGE
+    }
+  }
+
+  function providerLabel(p: Provider | string): string {
+    if (p === PROVIDER_OPENAI || p === PROVIDER_ANTHROPIC || p === PROVIDER_GEMINI) {
+      return t(`monitorCommon.providers.${p}`)
+    }
+    return p || '-'
+  }
+
+  function providerBadgeClass(p: Provider | string): string {
+    switch (p) {
+      case PROVIDER_OPENAI:
+        return 'bg-green-100 text-green-800 dark:bg-green-900/30 dark:text-green-300'
+      case PROVIDER_ANTHROPIC:
+        return 'bg-orange-100 text-orange-800 dark:bg-orange-900/30 dark:text-orange-300'
+      case PROVIDER_GEMINI:
+        return 'bg-blue-100 text-blue-800 dark:bg-blue-900/30 dark:text-blue-300'
+      default:
+        return NEUTRAL_BADGE
+    }
+  }
+
+  function formatLatency(ms: number | null | undefined): string {
+    if (ms == null) return t('monitorCommon.latencyEmpty')
+    return String(Math.round(ms))
+  }
+
+  function formatPercent(v: number | null | undefined): string {
+    if (v == null || Number.isNaN(v)) return '-'
+    return `${v.toFixed(2)}%`
+  }
+
+  function formatAvailability(row: AvailabilityRow): string {
+    if (!row.primary_status) return '-'
+    return formatPercent(row.availability_7d)
+  }
+
+  return {
+    statusLabel,
+    statusBadgeClass,
+    providerLabel,
+    providerBadgeClass,
+    formatLatency,
+    formatPercent,
+    formatAvailability,
+  }
+}