📎 上传 JSON 题库（支持单题与综合分析题）
超级管理员上传的题目会进入公共题库，所有已登录用户都能查看。
✅ 单题格式：{"text":"题干","options":{"A":"...","B":"..."},"correctLetter":"D","explanation":"解析","year":2025,"knowledge":"第一章"}
✅ 综合分析题格式：{"text":"背景材料","type":"comprehensive","subQuestions":[{"text":"(1)...","options":{...},"correctLetter":"ACE","explanation":"..."}],"year":null,"knowledge":"第三章"}