I want to have a “fullbright” effect in my 3d scene where all areas are lit up fully and no shadows are cast. I would like a simple solution which only requires putting a shader on the root node, camera, or viewport or creating a World Environment.
In your 3D camera you can add an environment, which has the option for ambient light. If you set the ambient source to Color and white with an energy of 1.0, I think you should have what you want as long as there are no other light sources contributing.