refactor(i18n): U21 Zabbix 组件 i18n 治理 — ZabbixDatasourceManager + ZabbixDashboard 从 i18n.t() 全局改为 useTranslation() hook

- ZabbixDatasourceManager.tsx (415L): 30 处 i18n.t()/硬编码中文清零, 删除 5 个 monitor.zabbixdatasourc.* hash 键, 新增 monitor.zabbixDs.* 语义化命名空间 (23 键)
- ZabbixDashboard.tsx (162L): 12 处 i18n.t()/硬编码中文清零, 删除 monitor.zabbixdashboard.* + monitor.prometheusdashb.s5e8eb212 hash 键, 修复 3 个中文幻影键 (i18n.t('磁盘') → t('monitor.zabbixDs.disk') 等)
- 新增 common.days/common.seconds 通用单位键
- 删除 monitor.zabbixdatasourc (5 hash 键) + monitor.zabbixdashboard (1 hash 键) + monitor.prometheusdashb.s5e8eb212 hash 键
- zh/en 6767=6767 对齐, tsc -b=0, npm build✓ (17.41s), ESLint=0/43/0/0, go build=0, 17/17 测试通过

frontend/src/locales/en-US.json

@@ -511,7 +511,9 @@
     "created": "Created",
     "severity": "Severity",
     "critical": "Critical",
-    "request.tokenExpired": "Session expired, please log in again"
+    "request.tokenExpired": "Session expired, please log in again",
+    "days": "days",
+    "seconds": "sec"
   },
   "menu": {
     "dashboard": "Dashboard",
@@ -4393,6 +4395,41 @@
       "wechat": "WeChat Work",
       "email": "Email",
       "sms": "SMS"
+    },
+    "zabbixDs": {
+      "title": "Zabbix Datasource",
+      "subtitle": "Configure Zabbix API connection to get host monitoring data",
+      "addDatasource": "Add Datasource",
+      "emptyState": "No Zabbix data sources",
+      "fetchListError": "Failed to fetch datasource list",
+      "urlRequired": "Please enter Zabbix API URL",
+      "datasourceSaved": "Datasource saved",
+      "deleteConfirm": "Are you sure to delete \"{{name}}\"?",
+      "setDefaultSuccess": "\"{{name}}\" set as default",
+      "deleteFailed": "Delete failed",
+      "editTitle": "Edit Zabbix Datasource",
+      "createTitle": "Create Zabbix Datasource",
+      "dialogDesc": "Configure Zabbix API connection for host monitoring and alert data",
+      "namePlaceholder": "e.g. Production Zabbix",
+      "apiAuth": "Zabbix API Authentication",
+      "trendsSettings": "Trends Settings",
+      "otherSettings": "Other Settings",
+      "directDbBadge": "Direct DB",
+      "disableAck": "Disable Acknowledges (Read-only User)",
+      "disableDataAlignment": "Disable Data Alignment",
+      "testConnection": "Test Connection",
+      "user": "User",
+      "loading": "Loading...",
+      "noHosts": "No monitored Zabbix hosts found",
+      "hostMonitor": "Zabbix Host Monitor",
+      "unit": "hosts",
+      "disk": "Disk",
+      "flowOut": "Out",
+      "problems": "Problems",
+      "totalHosts": "{{count}} hosts total",
+      "perPage": "/page",
+      "prevPage": "Prev",
+      "nextPage": "Next"
     }
   },
   "task": {