Create an architecture file for what lights could do

We need a file that lists the possible things that the lights could be used to display, so that we can focus on getting (some of) those things to work. Possible things we could display could include:
- Something about the robot, such as the position the grabber is in
- Scrolling text, like a short message about the team or an inspirational message
- A still image, like our logo or a planet
- An animated image, probably something to do with space like a rocket ship or a rover

No file, test, or entry point is named in the issue; first inspect the repository structure to choose where an architecture document belongs. Use the listed robot status, scrolling text, still-image, and animated-image capabilities as its sections; done when the file records these candidate display uses for planning.

Written by the indexing model from the issue text.