refactor(i18n): U24 Monitor 模块 i18n hook 迁移 — 26 个 .tsx 文件从全局 i18n.t() 迁移到 useTranslation() hook + 89 个 phantom 中文文本键替换为 monitor.lbl.* 语义化键

- 新增 monitor.lbl 翻译子命名空间 89 键（HostMonitor/Middleware/Site/SNMP/Shared）
- 26 .tsx: import i18n → useTranslation() hook + i18n.t('中文') → t('monitor.lbl.semanticKey')
- 模块级代码(TABS/METRIC_CATEGORIES)保留 i18n.t() + 语义化键
- 1 .ts helpers 文件 phantom 键替换
- zh/en 6886→6975 +89 键对齐
- tsc -b=0, npm build✓ (17.16s), ESLint=0/53/0, go build=0, Docker healthy

frontend/src/pages/monitor/site-monitor/SiteProtocolPieChart.tsx

@@ -6,7 +6,7 @@ import { Card, CardContent } from '@/components/ui/card';
 import { PieChart as PieChartIcon } from 'lucide-react';
 import { PROBE_TYPE_OPTIONS, normalizeProbeType } from './helpers';
 import type { SiteTask } from './helpers';
-import i18n from '@/i18n';
+import { useTranslation } from 'react-i18next';
 
 interface Props {
   tasks: SiteTask[];
@@ -21,6 +21,7 @@ const PROTOCOL_COLORS: Record<string, string> = {
 };
 
 export function SiteProtocolPieChart({ tasks }: Props) {
+  const { t } = useTranslation();
   const protocolData = useMemo(() => {
     const counts: Record<string, number> = {};
     for (const t of PROBE_TYPE_OPTIONS) counts[t] = 0;
@@ -36,7 +37,7 @@ export function SiteProtocolPieChart({ tasks }: Props) {
   if (tasks.length === 0) {
     return (
       <Card className="bg-[var(--dg-bg-secondary)] border-[var(--dg-border)]">
-        <CardContent className="p-6 text-center text-sm text-[var(--dg-text-muted)]"> {i18n.t('可用率(24h)')} </CardContent>
+        <CardContent className="p-6 text-center text-sm text-[var(--dg-text-muted)]"> {t('monitor.lbl.availability24h')} </CardContent>
       </Card>
     );
   }
@@ -46,7 +47,7 @@ export function SiteProtocolPieChart({ tasks }: Props) {
       <CardContent className="p-4">
         <div className="flex items-center gap-2 mb-2">
           <PieChartIcon className="h-4 w-4 text-[var(--dg-text-muted)]" />
-          <h3 className="text-sm font-medium text-[var(--dg-text-primary)]"> {i18n.t('可用率(24h)')} </h3>
+          <h3 className="text-sm font-medium text-[var(--dg-text-primary)]"> {t('monitor.lbl.availability24h')} </h3>
           <span className="text-[10px] text-[var(--dg-text-muted)]">共 {tasks.length} 个任务</span>
         </div>
         <ResponsiveContainer width="100%" height={200}>