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/schemas/notification.py

@@ -0,0 +1,51 @@
+"""
+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 pydantic import BaseModel, ConfigDict
+from datetime import datetime
+from typing import Optional, Dict
+from app.models.notification import NotificationType
+from uuid import UUID
+
+
+class NotificationResponse(BaseModel):
+    id: int
+    user_id: UUID
+    type: NotificationType
+    title: str
+    message: str
+    notification_metadata: Optional[Dict] = None
+    is_read: bool
+    created_at: datetime
+
+    class Config:
+        from_attributes = True
+
+
+class NotificationSettingsOut(BaseModel):
+    """A user's chat push preferences."""
+    notify_new_chat: bool
+    notify_chat_transfer: bool
+    notify_chat_assigned: bool
+
+    model_config = ConfigDict(from_attributes=True)
+
+
+class NotificationSettingsUpdate(BaseModel):
+    """Partial update — only the toggles the caller sent are applied."""
+    notify_new_chat: Optional[bool] = None
+    notify_chat_transfer: Optional[bool] = None
+    notify_chat_assigned: Optional[bool] = None