Android App to import and export categorizetion rule

- [x] I am on the [latest](https://github.com/ActivityWatch/activitywatch/releases/latest) ActivityWatch version.
- [x] I have searched the issues of this repo and believe that this is not a duplicate.

- **OS name and version**: Android 14-xiaomi hyperos1.0.4/Android 13-zui15
- **ActivityWatch version**: v0.12.1(both, in google play)

## Describe the bug
There are issues attempting to import and export categorization rules in the categorization options of the settings interface.
Clicking on import did not respond. clicking on export:
or flashback directly.

## Expected behavior
After clicking import, the corresponding JSON file can be found from the default file manager, and exporting can generate the corresponding JSON file