fix(ui): Add Back label in KOReader Sync screen (#770)
## Summary
- Remove duplicate Cancel option
- Add Back label
<img width="435" height="613" alt="image"
src="https://github.com/user-attachments/assets/a3af4133-46fa-46e6-8360-a15dd7c4fe2a"
/>
## Result
<img width="575" height="431" alt="image"
src="https://github.com/user-attachments/assets/6ccdac89-43df-45bf-bcfa-3a7cc4bd88e4"
/>
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### AI Usage
Did you use AI tools to help write this code? _**< PARTIALLY >**_
Closes #754