Ensure Consistent Category Colors

[JLambertazzo]

Closes #1668

Note

Was not able to accomplish reactivity in this PR. Disabling of other colors, in addition to displaying the error message, only shows up after a failed attempt to create the category.

Approach

• Added validation in the category.rb model which displays the message below when trying to select a color different from the parent category
• Grayed-out and disabled other colors when validation fails to reflect validation rule
  
• Once correct color is selected, category can be created
  

[zachgoll]

@JLambertazzo just an idea here—what if we used a simple Stimulus controller to hide the color picker entirely if the parent category field is populated, then on the backend, we simply use our internal logic to assign the parent color to the subcategory?

cc @justinfar in case you had other ideas here.

[JLambertazzo]

@JLambertazzo just an idea here—what if we used a simple Stimulus controller to hide the color picker entirely if the parent category field is populated, then on the backend, we simply use our internal logic to assign the parent color to the subcategory?

This worked really well! Here are the results:
Selection hides when parent is selected


Created subcategory is forced to have parent color

[zachgoll]

Looks good! Once conflicts are resolved, good to merge.

[JLambertazzo]

Completed merge, behavior seems to be the same!