update tools description & chat prompt
<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit
* **New Features**
* Updated the AFFiNE AI copilot system prompt to reflect support for
multiple AI providers and a more concise, structured format with clearer
guidelines and modular tags.
* **Enhancements**
* Improved descriptions for document search and reading tools, providing
clearer guidance on when and how to use keyword search, semantic search,
and document reading features.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
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 -->
