[Feature/Improvement] Mark Timers as Completed

### Checklist

- [x] I made sure that the issue I am raising doesn't already exist

### Use case / Problem

The app currently doesn’t track whether a timer or workout has been completed. When users create multiple workouts, they have no way to tell which ones they’ve already finished.

### Proposal / Solution

Allow the user to manually mark a timer as completed. Default behavior of the app should not be changed and it should be totally optional for the user to select "Mark completed".

There would be some visual indication on the home screen that the workout has been marked as completed. Such as a checkmark, green bar, etc.

Eventually, automatically marking as completed could be configurable in settings.

### Example Code

_No response_

### Platform

_No response_

### Audio Files/URLs/Sources

_No response_

### Mockups

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### Related issues / more information

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### Working on PR

yep