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/file_attachment.py

@@ -0,0 +1,95 @@
+"""
+Copyright 2024-2026 ChatterMate
+
+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.orm import Session
+from app.models.file_attachment import FileAttachment
+from typing import List, Optional
+from uuid import UUID
+
+
+class FileAttachmentRepository:
+    def __init__(self, db: Session):
+        self.db = db
+
+    def create_attachment(
+        self,
+        file_url: str,
+        filename: str,
+        content_type: str,
+        file_size: int,
+        organization_id: UUID,
+        chat_history_id: Optional[int] = None,
+        uploaded_by_user_id: Optional[UUID] = None,
+        uploaded_by_customer_id: Optional[UUID] = None
+    ) -> FileAttachment:
+        """Create a new file attachment record"""
+        attachment = FileAttachment(
+            file_url=file_url,
+            filename=filename,
+            content_type=content_type,
+            file_size=file_size,
+            chat_history_id=chat_history_id,
+            organization_id=organization_id,
+            uploaded_by_user_id=uploaded_by_user_id,
+            uploaded_by_customer_id=uploaded_by_customer_id
+        )
+        self.db.add(attachment)
+        self.db.commit()
+        self.db.refresh(attachment)
+        return attachment
+
+    def get_attachment(self, attachment_id: int) -> Optional[FileAttachment]:
+        """Get a file attachment by ID"""
+        return self.db.query(FileAttachment).filter(
+            FileAttachment.id == attachment_id
+        ).first()
+
+    def get_attachments_by_chat_history(
+        self, chat_history_id: int
+    ) -> List[FileAttachment]:
+        """Get all attachments for a chat message"""
+        return self.db.query(FileAttachment).filter(
+            FileAttachment.chat_history_id == chat_history_id
+        ).all()
+
+    def get_attachments_by_organization(
+        self, organization_id: UUID, limit: int = 100
+    ) -> List[FileAttachment]:
+        """Get all attachments for an organization"""
+        return self.db.query(FileAttachment).filter(
+            FileAttachment.organization_id == organization_id
+        ).order_by(FileAttachment.created_at.desc()).limit(limit).all()
+
+    def delete_attachment(self, attachment_id: int) -> bool:
+        """Delete a file attachment"""
+        attachment = self.get_attachment(attachment_id)
+        if attachment:
+            self.db.delete(attachment)
+            self.db.commit()
+            return True
+        return False
+
+    def link_attachment_to_message(
+        self, attachment_id: int, chat_history_id: int
+    ) -> Optional[FileAttachment]:
+        """Link an existing attachment to a chat message"""
+        attachment = self.get_attachment(attachment_id)
+        if attachment:
+            attachment.chat_history_id = chat_history_id
+            self.db.commit()
+            self.db.refresh(attachment)
+            return attachment
+        return None