refactor(usermanagement): 修改教师布局权限控制

- 将 TeacherLayout 组件的允许角色从 ["ADMIN", "TEACHER"] 修改为仅 ["ADMIN"]
- 此修改限制了只有管理员可以访问教师管理功能

src/app/(app)/usermanagement/teacher/layout.tsx

@@ -1,5 +1,5 @@
 import ProtectedLayout from "../_components/ProtectedLayout";
 
 export default function TeacherLayout({ children }: { children: React.ReactNode }) {
-  return <ProtectedLayout allowedRoles={["ADMIN", "TEACHER"]}>{children}</ProtectedLayout>;
+  return <ProtectedLayout allowedRoles={["ADMIN"]}>{children}</ProtectedLayout>;
 }