Pydantic: type hints that DO something

No more playground

Every module until now built throwaway code โ€” a mini Flask app, a Django project you'll never deploy. Starting here, the textbook is apps/backend itself. You'll read the actual files that serve your iOS app, extend them in browser exercises, and (via terminal checklists) run the real server and the real test suite.

First stop: Pydantic. It's the library that makes every model in app/schemas.py tick.