[Feature/Improvement] Custom Hyperlink Field for Exercises

### Checklist

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

### Use case / Problem

Users currently have to leave the app to search for a reference video for exercises. Allow users to link personal YouTube videos or instructional clips to refresh their form before starting an interval.

### Proposal / Solution

- Add a "URL" or "Video Link" field within the exercise edit screen.
- Place a clickable icon or hyperlink on the main dashboard for each exercise.

### Example Code

_No response_

### Platform

_No response_

### Audio Files/URLs/Sources

_No response_

### Mockups

_No response_

### Related issues / more information

_No response_

### Working on PR

yep