fix: resolve E2E audit findings and add Phase C frontend pages

- Fix audit_log handler multi-tenant bug: use Extension<TenantContext>
  instead of hardcoded default_tenant_id
- Fix sendMessage route mismatch: frontend /messages/send → /messages
- Add POST /users/{id}/roles backend route for role assignment
- Add task.completed event payload: started_by + instance_id for
  notification delivery
- Add audit log viewer frontend page (AuditLogViewer.tsx)
- Add language management frontend page (LanguageManager.tsx)
- Add api/auditLogs.ts and api/languages.ts modules

apps/web/src/pages/Settings.tsx

@@ -1,17 +1,21 @@
 import { Tabs } from 'antd';
 import DictionaryManager from './settings/DictionaryManager';
+import LanguageManager from './settings/LanguageManager';
 import MenuConfig from './settings/MenuConfig';
 import NumberingRules from './settings/NumberingRules';
 import SystemSettings from './settings/SystemSettings';
 import ThemeSettings from './settings/ThemeSettings';
+import AuditLogViewer from './settings/AuditLogViewer';
 
 const Settings: React.FC = () => {
   const items = [
     { key: 'dictionaries', label: '数据字典', children: <DictionaryManager /> },
+    { key: 'languages', label: '语言管理', children: <LanguageManager /> },
     { key: 'menus', label: '菜单配置', children: <MenuConfig /> },
     { key: 'numbering', label: '编号规则', children: <NumberingRules /> },
     { key: 'settings', label: '系统参数', children: <SystemSettings /> },
     { key: 'theme', label: '主题设置', children: <ThemeSettings /> },
+    { key: 'audit-log', label: '审计日志', children: <AuditLogViewer /> },
   ];
 
   return <Tabs defaultActiveKey="dictionaries" items={items} />;