Alembic migrations

Migrations are version control for your schema

Module 21 called this out for Django (makemigrations/migrate). The real backend uses Alembic, SQLAlchemy's migration tool, for the exact same job: every change to models_db.py needs a matching migration file that tells the database HOW to change its actual tables to match.

alembic/env.py wires this to the app's own models and settings, so migrations are always generated against the real models_db.py and the real database_url — no separate config to keep in sync: