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/notification.py

@@ -0,0 +1,47 @@
+"""
+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, JSON, DateTime, ForeignKey, Boolean, Enum as SQLEnum
+from sqlalchemy.orm import relationship
+from sqlalchemy.sql import func
+from app.database import Base
+import enum
+from sqlalchemy.dialects.postgresql import UUID
+
+class NotificationType(str, enum.Enum):
+    KNOWLEDGE_PROCESSED = "knowledge_processed"
+    KNOWLEDGE_FAILED = "knowledge_failed"
+    FAQ_GENERATED = "faq_generated"
+    FAQ_GENERATION_FAILED = "faq_generation_failed"
+    SYSTEM = "system"
+    CHAT = "chat"
+
+
+class Notification(Base):
+    __tablename__ = "notifications"
+
+    id = Column(Integer, primary_key=True, index=True)
+    user_id = Column(UUID(as_uuid=True), ForeignKey("users.id"), nullable=False)
+    type = Column(SQLEnum(NotificationType), nullable=False)
+    title = Column(String, nullable=False)
+    message = Column(String, nullable=False)
+    # For additional data like queue_id, knowledge_id etc
+    notification_metadata = Column(JSON, nullable=True)
+    is_read = Column(Boolean, default=False)
+    created_at = Column(DateTime(timezone=True), server_default=func.now())
+
+    # Relationships
+    user = relationship("User", back_populates="notifications")