feat: 添加双人对练功能

- 新增数据库迁移脚本 (practice_rooms, practice_room_messages)
- 新增后端 API: 房间创建/加入/消息同步/报告生成
- 新增前端页面: 入口页/对练房间/报告页
- 新增 AI 双人评估服务和提示词

backend/app/models/practice_room.py

@@ -0,0 +1,122 @@
+"""
+双人对练房间模型
+
+功能：
+- 房间管理（创建、加入、状态）
+- 参与者管理
+- 实时消息同步
+"""
+from sqlalchemy import Column, Integer, String, Text, Boolean, DateTime, ForeignKey, JSON
+from sqlalchemy.sql import func
+from sqlalchemy.orm import relationship
+from app.models.base import Base
+
+
+class PracticeRoom(Base):
+    """双人对练房间模型"""
+    __tablename__ = "practice_rooms"
+    
+    id = Column(Integer, primary_key=True, index=True, comment="房间ID")
+    room_code = Column(String(10), unique=True, nullable=False, index=True, comment="6位邀请码")
+    room_name = Column(String(200), comment="房间名称")
+    
+    # 场景信息
+    scene_id = Column(Integer, ForeignKey("practice_scenes.id", ondelete="SET NULL"), comment="关联场景ID")
+    scene_name = Column(String(200), comment="场景名称")
+    scene_type = Column(String(50), comment="场景类型")
+    scene_background = Column(Text, comment="场景背景")
+    
+    # 角色设置
+    role_a_name = Column(String(50), default="角色A", comment="角色A名称（如销售顾问）")
+    role_b_name = Column(String(50), default="角色B", comment="角色B名称（如顾客）")
+    role_a_description = Column(Text, comment="角色A描述")
+    role_b_description = Column(Text, comment="角色B描述")
+    
+    # 参与者信息
+    host_user_id = Column(Integer, ForeignKey("users.id", ondelete="CASCADE"), nullable=False, comment="房主用户ID")
+    guest_user_id = Column(Integer, ForeignKey("users.id", ondelete="SET NULL"), comment="加入者用户ID")
+    host_role = Column(String(10), default="A", comment="房主选择的角色(A/B)")
+    max_participants = Column(Integer, default=2, comment="最大参与人数")
+    
+    # 状态和时间
+    status = Column(String(20), default="waiting", index=True, comment="状态: waiting/ready/practicing/completed/canceled")
+    created_at = Column(DateTime, server_default=func.now(), comment="创建时间")
+    started_at = Column(DateTime, comment="开始时间")
+    ended_at = Column(DateTime, comment="结束时间")
+    duration_seconds = Column(Integer, default=0, comment="对练时长（秒）")
+    
+    # 对话统计
+    total_turns = Column(Integer, default=0, comment="总对话轮次")
+    role_a_turns = Column(Integer, default=0, comment="角色A发言次数")
+    role_b_turns = Column(Integer, default=0, comment="角色B发言次数")
+    
+    # 软删除
+    is_deleted = Column(Boolean, default=False, comment="是否删除")
+    deleted_at = Column(DateTime, comment="删除时间")
+    
+    def __repr__(self):
+        return f"<PracticeRoom(code='{self.room_code}', status='{self.status}')>"
+    
+    @property
+    def is_full(self) -> bool:
+        """房间是否已满"""
+        return self.guest_user_id is not None
+    
+    @property
+    def participant_count(self) -> int:
+        """当前参与人数"""
+        count = 1  # 房主
+        if self.guest_user_id:
+            count += 1
+        return count
+    
+    def get_user_role(self, user_id: int) -> str:
+        """获取用户在房间中的角色"""
+        if user_id == self.host_user_id:
+            return self.host_role
+        elif user_id == self.guest_user_id:
+            return "B" if self.host_role == "A" else "A"
+        return None
+    
+    def get_role_name(self, role: str) -> str:
+        """获取角色名称"""
+        if role == "A":
+            return self.role_a_name
+        elif role == "B":
+            return self.role_b_name
+        return None
+    
+    def get_user_role_name(self, user_id: int) -> str:
+        """获取用户的角色名称"""
+        role = self.get_user_role(user_id)
+        return self.get_role_name(role) if role else None
+
+
+class PracticeRoomMessage(Base):
+    """房间实时消息模型"""
+    __tablename__ = "practice_room_messages"
+    
+    id = Column(Integer, primary_key=True, index=True, comment="消息ID")
+    room_id = Column(Integer, ForeignKey("practice_rooms.id", ondelete="CASCADE"), nullable=False, index=True, comment="房间ID")
+    user_id = Column(Integer, ForeignKey("users.id", ondelete="SET NULL"), comment="发送者用户ID")
+    message_type = Column(String(20), nullable=False, comment="消息类型: chat/system/join/leave/start/end")
+    content = Column(Text, comment="消息内容")
+    role_name = Column(String(50), comment="角色名称")
+    sequence = Column(Integer, nullable=False, comment="消息序号")
+    created_at = Column(DateTime(3), server_default=func.now(3), comment="创建时间")
+    
+    def __repr__(self):
+        return f"<PracticeRoomMessage(room_id={self.room_id}, type='{self.message_type}', seq={self.sequence})>"
+    
+    def to_dict(self) -> dict:
+        """转换为字典（用于SSE推送）"""
+        return {
+            "id": self.id,
+            "room_id": self.room_id,
+            "user_id": self.user_id,
+            "message_type": self.message_type,
+            "content": self.content,
+            "role_name": self.role_name,
+            "sequence": self.sequence,
+            "created_at": self.created_at.isoformat() if self.created_at else None
+        }