MySpool web: Amplify, Python 3.12 Lambdas

The sensor app came back as a Flutter web application on Amplify, with a collaborator owning the backend. The Lambdas moved to Python 3.12 and were split by responsibility, one function per device-management concern instead of one handler for everything.

What carried over from 2021 was the stack, not the backend: Flutter, Amplify and Cognito sign-in, in a new Amplify project with its own user pool. Separate functions also meant two people could change the backend without touching the same code.