Describe the bug
Sometimes it is possible to add a color property twice (eg. two "ExcludingDaysLabel" colors. This shouldn't be allowed.

To Reproduce
Steps to reproduce the behavior:

1. Visit the demo site - https://streak-stats.demolab.com/demo/
2. Expand "Advanced Options"
3. Click the add property (+) button 11 times (until all properties are added)
4. Click the remove (−) button next to the "Dates" property
5. Click the add property (+) button while "ExcludingDaysLabel" is selected in the menu
6. "ExcludingDaysLabel" gets added again even though it's already added

Expected behavior
Properties already added should not appear in the dropdown.

Screenshots
If applicable, add screenshots to help explain your problem.

Desktop (please complete the following information):

OS: Arch Linux
Browser: Brave
Version: 1.57.47

Smartphone (please complete the following information):

• Device: Pixel 6
• OS: Android 14 beta
• Browser: Brave
• Version: 1.57.60