feat(server): add comment-attachment model (#12909)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **New Features**
* Introduced support for comment attachments, allowing users to add,
view, and manage attachments linked to comments within documents.
* **Tests**
* Added comprehensive tests to ensure correct behavior for adding,
updating, deleting, listing, and retrieving comment attachments.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->


#### PR Dependency Tree


* **PR #12909** 👈
  * **PR #12911**
    * **PR #12761**
      * **PR #12924**
        * **PR #12925**

This tree was auto-generated by
[Charcoal](https://github.com/danerwilliams/charcoal)

packages/backend/server/src/models/index.ts

@@ -8,6 +8,7 @@ import { ModuleRef } from '@nestjs/core';
 
 import { ApplyType } from '../base';
 import { CommentModel } from './comment';
+import { CommentAttachmentModel } from './comment-attachment';
 import { AppConfigModel } from './config';
 import { CopilotContextModel } from './copilot-context';
 import { CopilotJobModel } from './copilot-job';
@@ -50,6 +51,7 @@ const MODELS = {
   copilotJob: CopilotJobModel,
   appConfig: AppConfigModel,
   comment: CommentModel,
+  commentAttachment: CommentAttachmentModel,
 };
 
 type ModelsType = {
@@ -102,6 +104,7 @@ const ModelsSymbolProvider: ExistingProvider = {
 export class ModelsModule {}
 
 export * from './comment';
+export * from './comment-attachment';
 export * from './common';
 export * from './copilot-context';
 export * from './copilot-job';