feat(models): 组织、用户、角色、客户、会话与消息模型

按组织边界定义数据关系，补齐仓储层与通用工具，迁移脚本可重复执行。

backend/app/models/user.py

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+"""
+Copyright 2024-2026 ReplyPier
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+"""
+
+from sqlalchemy import Column, Integer, String, Boolean, DateTime, ForeignKey, func, Table, Text
+from sqlalchemy.orm import relationship
+from sqlalchemy.dialects.postgresql import UUID
+import uuid
+from app.database import Base
+from passlib.context import CryptContext
+from sqlalchemy.sql import func
+
+pwd_context = CryptContext(schemes=["bcrypt"], deprecated="auto")
+
+# Association table for many-to-many relationship between users and groups
+user_groups = Table(
+    'user_groups',
+    Base.metadata,
+    Column('user_id', UUID(as_uuid=True), ForeignKey('users.id'), primary_key=True),
+    Column('group_id', UUID(as_uuid=True), ForeignKey('groups.id'), primary_key=True)
+)
+
+class UserGroup(Base):
+    __tablename__ = "groups"
+
+    id = Column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+    name = Column(String, nullable=False)
+    description = Column(String)
+    organization_id = Column(UUID(as_uuid=True), ForeignKey("organizations.id"), nullable=False)
+    created_at = Column(DateTime, server_default=func.now())
+    updated_at = Column(DateTime, server_default=func.now(), onupdate=func.now())
+
+    # Relationships
+    organization = relationship("Organization", back_populates="groups")
+    users = relationship("User", secondary=user_groups, back_populates="groups")
+    session_assignments = relationship("SessionToAgent", back_populates="group")
+
+    # agents relationship will be created by backref from Agent model
+
+    def to_dict(self):
+        """Convert user group object to dictionary"""
+        return {
+            "id": str(self.id),
+            "name": self.name,
+            "description": self.description,
+            "agents": [{"id": str(agent.id), "name": agent.name} for agent in self.agents]
+        }
+
+class User(Base):
+    __tablename__ = "users"
+
+    id = Column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+    email = Column(String, unique=True, index=True)
+    full_name = Column(String)
+    hashed_password = Column(String)
+    is_active = Column(Boolean, default=True)
+    profile_pic = Column(String, nullable=True)
+    is_online = Column(Boolean, default=False)
+    last_seen = Column(DateTime(timezone=True), server_default=func.now(), onupdate=func.now())
+    organization_id = Column(UUID(as_uuid=True), ForeignKey("organizations.id"), nullable=True)
+    role_id = Column(Integer, ForeignKey("roles.id"), nullable=True)
+    created_at = Column(DateTime(timezone=True), server_default=func.now())
+    updated_at = Column(DateTime(timezone=True), onupdate=func.now())
+
+    # Define relationships
+    organization = relationship("Organization", back_populates="users")
+    role = relationship("Role", back_populates="users")
+    knowledge_queue_items = relationship(
+        "KnowledgeQueue",
+        back_populates="user",
+        cascade="all, delete-orphan"
+    )
+    notifications = relationship(
+        "Notification", back_populates="user", cascade="all, delete-orphan")
+    # One row per signed-in browser; see app/models/fcm_token.py
+    fcm_tokens = relationship(
+        "FCMToken", back_populates="user", cascade="all, delete-orphan")
+    chat_histories = relationship("ChatHistory", back_populates="user")
+    
+    # Add groups relationship
+    groups = relationship("UserGroup", secondary=user_groups, back_populates="users")
+
+    # Add this new relationship
+    session_assignments = relationship("SessionToAgent", back_populates="user")
+    ratings = relationship("Rating", back_populates="user")
+    def to_dict(self):
+        """Convert user object to dictionary"""
+        return {
+            "id": str(self.id),
+            "email": self.email,
+            "full_name": self.full_name,
+            "is_active": self.is_active,
+            "organization_id": str(self.organization_id),
+            "created_at": self.created_at,
+            "updated_at": self.updated_at,
+            "role": self.role.to_dict() if self.role else None
+        }
+
+    def verify_password(self, password: str) -> bool:
+        return pwd_context.verify(password, self.hashed_password)
+
+    @staticmethod
+    def get_password_hash(password: str) -> str:
+        return pwd_context.hash(password)