Containerize with Docker

Same code, same result, anywhere

"It works on my machine" is a real failure mode: your laptop has Python 3.12, a .venv full of exact package versions, and an OS that happens to have the right system libraries. The server that runs your app in production has none of that guaranteed. A container is a bundle of the app plus everything it needs to run — the Python interpreter, the exact dependency versions, the OS libraries — packaged so it behaves identically on your laptop, in CI, and in production.

Docker is the tool that builds and runs containers from a recipe called a Dockerfile. PawWalk's backend (the FastAPI app you've been building since module 23) is about to get one.