feat(server): add read doc tool (#12811)

close AI-186















#### PR Dependency Tree


* **PR #12811** 👈

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

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

- **New Features**
- Added a new tool enabling users to read document content and metadata
within a workspace, with enforced access control.
- **Improvements**
- Updated tool interfaces and outputs to support the document reading
functionality seamlessly.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

packages/backend/server/src/plugins/copilot/tools/index.ts

@@ -1,5 +1,6 @@
 export * from './doc-edit';
 export * from './doc-keyword-search';
+export * from './doc-read';
 export * from './doc-semantic-search';
 export * from './error';
 export * from './exa-crawl';