Close [AI-410](https://linear.app/affine-design/issue/AI-410)
<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit
- New Features
- None
- Bug Fixes
- Middle-click panning now reliably returns to the previously active
tool, including after using Copilot or frame navigation.
- Smoother, more responsive transition into panning to reduce accidental
selections.
- Refactor
- Simplified AI panel click-outside handling with no change to
user-visible behavior.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->