Architectural overview(s) and execution paths

[LlGC-jop]

After a short discussion between a few of us at NLW we think it would be very useful to current and future developers to have a written and visual depiction of how the UV functions, so that it's easier to know where to start and understand where any work needs to take place.

[demiankatz]

Agreed, though I think the challenge is deciding on the level of abstraction for such documentation, since I could imagine the architecture changing significantly through upcoming modernization efforts. Probably best to start at a very high level if possible, to minimize the impact of future changes.