Blueprints & error handlers

One app.py won't survive contact with a real API

Right now app.py holds walker routes AND booking routes in one file. That's fine for two resources. PawWalk's real backend has walkers, bookings, pets, payments, auth, an AI assistant — a dozen resources. One file would become an unreadable, un-mergeable wall of routes.

Flask's answer is a blueprint: a mini Flask app for one resource's routes, defined in its own file, then registered onto the main app. It's the same instinct as splitting a giant SwiftUI view into smaller ones — one concern per file.