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_settings.py

@@ -0,0 +1,58 @@
+"""
+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 Boolean, Column, DateTime, ForeignKey
+from sqlalchemy.dialects.postgresql import UUID
+from sqlalchemy.orm import relationship
+from sqlalchemy.sql import expression, func
+
+from app.database import Base
+
+# Preference column per chat event, and the value assumed for a user who has
+# no row yet. Transfer/assignment default on so existing users keep the
+# notifications they already get; new-chat is opt-in because it fires on every
+# conversation, including the ones the AI handles alone.
+NOTIFY_NEW_CHAT = "notify_new_chat"
+NOTIFY_CHAT_TRANSFER = "notify_chat_transfer"
+NOTIFY_CHAT_ASSIGNED = "notify_chat_assigned"
+
+NOTIFICATION_PREFERENCE_DEFAULTS = {
+    NOTIFY_NEW_CHAT: False,
+    NOTIFY_CHAT_TRANSFER: True,
+    NOTIFY_CHAT_ASSIGNED: True,
+}
+
+
+class UserNotificationSettings(Base):
+    """Per-user chat push preferences. One row per user, created lazily with
+    defaults on first read — absence of a row means the defaults above apply.
+    """
+    __tablename__ = "user_notification_settings"
+
+    user_id = Column(
+        UUID(as_uuid=True),
+        ForeignKey("users.id", ondelete="CASCADE"),
+        primary_key=True,
+    )
+
+    notify_new_chat = Column(Boolean, nullable=False, default=False, server_default=expression.false())
+    notify_chat_transfer = Column(Boolean, nullable=False, default=True, server_default=expression.true())
+    notify_chat_assigned = Column(Boolean, nullable=False, default=True, server_default=expression.true())
+
+    created_at = Column(DateTime(timezone=True), server_default=func.now())
+    updated_at = Column(DateTime(timezone=True), onupdate=func.now())
+
+    user = relationship("User")