新增作文区与 AI 解读开关，修复 CSV 导出。

系统设置可关闭成绩复盘 AI；学生详情增加作文区（OCR/手动题目、方案与范文、历史与 MD 下载）；导出改用 UTF-8 文件名响应。

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/app/routers/exams.py

@@ -6,7 +6,7 @@ from sqlalchemy.orm import Session, joinedload
 
 from app.core.database import get_db
 from app.core.deps import get_current_user
-from app.models.user import ExamRecord, SubjectScore, User
+from app.models.user import ExamRecord, SubjectScore, SystemSettings, User
 from app.schemas import (
     ExamCreate,
     ExamOut,
@@ -322,6 +322,10 @@ async def review_insight(
     current_user: User = Depends(get_current_user),
 ):
     student = get_student_for_user(db, student_id, current_user.id)
+    settings_row = db.get(SystemSettings, 1)
+    if settings_row is not None and not getattr(settings_row, "ai_review_enabled", True):
+        raise HTTPException(status_code=status.HTTP_403_FORBIDDEN, detail="AI 复盘解读已在系统设置中关闭")
+
     exams = (
         db.query(ExamRecord)
         .options(joinedload(ExamRecord.scores).joinedload(SubjectScore.subject))