feat: 初始化考培练系统项目

- 从服务器拉取完整代码
- 按框架规范整理项目结构
- 配置 Drone CI 测试环境部署
- 包含后端(FastAPI)、前端(Vue3)、管理端

技术栈: Vue3 + TypeScript + FastAPI + MySQL

backend/app/models/exam_mistake.py

@@ -0,0 +1,43 @@
+"""
+错题记录模型
+"""
+from sqlalchemy import Column, Integer, ForeignKey, Text, DateTime, func
+from sqlalchemy.orm import relationship
+from datetime import datetime
+from app.models.base import BaseModel
+
+
+class ExamMistake(BaseModel):
+    """错题记录表"""
+    __tablename__ = "exam_mistakes"
+    
+    # 核心关联字段
+    user_id = Column(Integer, ForeignKey("users.id", ondelete="CASCADE"), nullable=False, index=True, comment="用户ID")
+    exam_id = Column(Integer, ForeignKey("exams.id", ondelete="CASCADE"), nullable=False, index=True, comment="考试ID")
+    question_id = Column(Integer, ForeignKey("questions.id", ondelete="SET NULL"), nullable=True, index=True, comment="题目ID（AI生成的题目可能为空）")
+    knowledge_point_id = Column(Integer, ForeignKey("knowledge_points.id", ondelete="SET NULL"), nullable=True, index=True, comment="关联的知识点ID")
+    
+    # 题目核心信息
+    question_content = Column(Text, nullable=False, comment="题目内容")
+    correct_answer = Column(Text, nullable=False, comment="正确答案")
+    user_answer = Column(Text, nullable=True, comment="用户答案")
+    question_type = Column(Text, nullable=True, index=True, comment="题型(single/multiple/judge/blank/essay)")
+    
+    # 掌握状态和统计字段
+    mastery_status = Column(Text, nullable=False, default='unmastered', index=True, comment="掌握状态: unmastered-未掌握, mastered-已掌握")
+    difficulty = Column(Text, nullable=False, default='medium', index=True, comment="题目难度: easy-简单, medium-中等, hard-困难")
+    wrong_count = Column(Integer, nullable=False, default=1, comment="错误次数统计")
+    mastered_at = Column(DateTime, nullable=True, comment="标记掌握时间")
+    
+    # 审计字段（继承自BaseModel，但这里重写以匹配数据库实际结构）
+    created_at = Column(DateTime, nullable=False, server_default=func.now(), comment="创建时间（北京时间）")
+    updated_at = Column(DateTime, nullable=False, server_default=func.now(), onupdate=func.now(), comment="更新时间（北京时间）")
+    
+    # 关系
+    user = relationship("User", backref="exam_mistakes")
+    exam = relationship("Exam", backref="mistakes")
+    question = relationship("Question", backref="mistake_records")
+    knowledge_point = relationship("KnowledgePoint", backref="mistake_records")
+    
+    def __repr__(self):
+        return f"<ExamMistake(id={self.id}, user_id={self.user_id}, exam_id={self.exam_id})>"