Moves the modules in lib/ to app/models and lib/integrations to app/integrations.

We decide on app/lib v. lib/ once and for all

It is also worth noting that lib/tasks typically has application-specific tasks, thus not fitting into the condition for lib. Which makes me question the criteria for lib

lib/ is intended to be for non-app specific library code that just happens to live in the app for now (usually pending extraction into open source or whatever).

Stuff like a generic PhoneNumberFormatter is exactly what lib/ is intended for.

If application code lives in app, then doesn't that imply that things in lib (such as PhoneNumberFormatter) are not application code? I think that's one of the reasons why your recommendation of app/lib felt right to me -- my classes feel like they belong in app somewhere.