feat(system):优化后端

1.新增后端测试
2.增加了后端的加密
3.增加了i18n（国际化）

frontend/src/App.tsx

@@ -1,4 +1,5 @@
 import { useEffect } from 'react';
+import i18n from './i18n';
 import { TopBar } from './components/Layout/TopBar';
 import { CollapsibleSidebar } from './components/Layout/CollapsibleSidebar';
 import { SettingsLayout } from './components/Settings/SettingsLayout';
@@ -22,6 +23,7 @@ function App() {
     workTab,
     agentTab,
     applyTheme,
+    locale,
   } = useAppStore();
 
   const { loadSessions } = useChatStore();
@@ -35,6 +37,13 @@ function App() {
     return () => mediaQuery.removeEventListener('change', handler);
   }, [applyTheme]);
 
+  // Sync persisted locale to i18next on mount
+  useEffect(() => {
+    if (locale && i18n.language !== locale) {
+      i18n.changeLanguage(locale);
+    }
+  }, [locale]);
+
   // Check auth and load sessions
   useEffect(() => {
     const token = localStorage.getItem('token');