Routes that return JSON

A dict is already almost JSON

Module 15 planted this flag: a JSON object is a dict. Flask cashes that in directly — return a dict from a route function, and Flask turns it into a proper JSON HTTP response for you, Content-Type header included.

Let's serve the same shape the real backend's GET /walkers returns — you can compare them side by side at http://localhost:8000/docs once the real backend is running.