[FEAT] Add Import Functionality for Exercises

[FalkenDev]

Is your feature request related to a problem? Please describe.

I want to quickly add pre-defined exercises to my library, but there is no way to import them from a file.

Describe the solution you'd like

I would like the ability to import exercises from a JSON file.

This feature could be added to the "Exercise Library" section with an "Import" button.

Describe alternatives you've considered

Manually adding exercises one by one, but this is time-consuming.

Why is this feature important to you?

This feature would save time when setting up my exercise library, especially if I have a large number of exercises to add.

Additional context

None.

✅ Checklist

• I have searched the existing issues and have not found a similar feature request.
• I am willing to work on this feature myself. (Optional)
• I have read and agree to the project's Code of Conduct.