(FWE) Getting started pt. 4 - Refactor architecture 'case study' to be a FWE section

[ericwindmill]

Describe the problem

Currently, the "case study" version of the architecture guidance lives in the architecture section of the docs. Given that this is a tutorial that's valuable for beginners, it should be moved to FWE.

Expected fix

• Massage the content to fit the page structure of FWE.
• Move the content to /getting-started/learn (or whatever)

On which browser(s) did you experience this issue?

No response

Additional context

No response

I would like to fix this problem.

• [ ] I will try and fix this problem on docs.flutter.dev.