### What problem does this PR solve?
Feature：Add a loading status to the agent canvas page.
### Type of change
- [x] New Feature (non-breaking change which adds functionality)
### What problem does this PR solve?
https://github.com/infiniflow/ragflow/issues/8157
The current master code should work fine, but hI ave some warnings, so I
added a declare to improve the warning
### Type of change
- [x] Bug Fix (non-breaking change which fixes an issue)
