[TB] Implement Dark Mode color editing

[aaronreed708]

Problem/Concern

Related to #820. After reviewing the wireframe and talking with @lwnoble, there is a requirement to allow users to modify their dark mode colors similar to how light mode colors can be changed now (e.g. selecting new colors from a dropdown). Currently, dark mode colors are auto generated by Theme Builder based on the corresponding light mode color.

As the current dark mode colors are only changed due to a light mode color change, all calculations will be run once and there is no worry about dark mode changes affecting down stream components because those will already be re-calculated due to the change of the light mode color. If we break this linkage and allow dark mode colors to be changed independent of light mode colors, I'm more leery that the user might get themselves into a bad state that we are then going to have to figure out how to prevent. But perhaps all this will need to succeed is a dark mode path that is parallel to the light mode path for figuring out dependencies and what might break and just handling them the same way in the dark mode case.

So in an abundance of caution and with agreement from @lwnoble , we are going to forego this requirement in the MVP for #820 and handle this issue after the other issues associated with that epic are stable.

Proposed Solution

Implement the wireframes here: https://www.figma.com/design/Co8gYdDmE64Wv90eWy9FwE/Mentorship---Edit-Theme-Builder-Colors-and-Themes?node-id=201-64193&t=Apr853j3wmXxgTi0-4