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/repositories/notification_settings.py

@@ -0,0 +1,86 @@
+"""
+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 typing import Iterable, List, Optional, Set
+from uuid import UUID
+
+from sqlalchemy.exc import IntegrityError
+from sqlalchemy.orm import Session
+
+from app.utils.uuids import as_uuid
+from app.models.notification_settings import (
+    NOTIFICATION_PREFERENCE_DEFAULTS,
+    UserNotificationSettings,
+)
+
+
+class UserNotificationSettingsRepository:
+    def __init__(self, db: Session):
+        self.db = db
+
+    def get(self, user_id: UUID | str) -> Optional[UserNotificationSettings]:
+        return (
+            self.db.query(UserNotificationSettings)
+            .filter(UserNotificationSettings.user_id == as_uuid(user_id))
+            .first()
+        )
+
+    def get_or_create(self, user_id: UUID | str) -> UserNotificationSettings:
+        settings = self.get(user_id)
+        if settings is None:
+            settings = UserNotificationSettings(user_id=as_uuid(user_id))
+            self.db.add(settings)
+            try:
+                self.db.commit()
+                self.db.refresh(settings)
+            except IntegrityError:
+                # Two concurrent first-reads (e.g. two tabs) race on the
+                # user_id PK; the loser re-reads the row the winner inserted
+                # rather than surfacing a 500.
+                self.db.rollback()
+                settings = self.get(user_id)
+        return settings
+
+    def filter_enabled(self, user_ids: Iterable[UUID | str], field: str) -> Set[UUID]:
+        """Of `user_ids`, return those who want notifications for `field`.
+
+        One query regardless of recipient count — transfer fans out to a whole
+        group and new chats fan out across the org. Users with no row yet fall
+        back to the column default rather than being dropped, so nothing has to
+        be backfilled.
+        """
+        if field not in NOTIFICATION_PREFERENCE_DEFAULTS:
+            raise ValueError(f"Unknown notification preference: {field}")
+
+        candidates = {as_uuid(user_id) for user_id in user_ids if user_id}
+        if not candidates:
+            return set()
+
+        rows = (
+            self.db.query(
+                UserNotificationSettings.user_id,
+                getattr(UserNotificationSettings, field),
+            )
+            .filter(UserNotificationSettings.user_id.in_(candidates))
+            .all()
+        )
+
+        stored = {user_id: enabled for user_id, enabled in rows}
+        default = NOTIFICATION_PREFERENCE_DEFAULTS[field]
+        return {
+            user_id for user_id in candidates
+            if stored.get(user_id, default)
+        }