### What problem does this PR solve?
Fix: PDF chunking issue for single-page documents
Refactor: Change the default refresh frequency to 5
Fix: Add a 0-degree threshold; require other rotation angles to exceed
it by at least 0.2
Fix: Put connector name tips to correct place
Fix: incorrect example response in delete datasets.
### Type of change
- [x] Bug Fix (non-breaking change which fixes an issue)
- [x] Refactoring