Database migrations

This directory is reserved for the database-backed progress and authentication migration set.

The current application uses storage.py and a local JSON state file. Before public multi-user deployment:

1. Introduce a repository abstraction behind storage.py.
2. Use SQLite for single-instance installations and PostgreSQL for hosted deployments.
3. Add migrations for users, refresh tokens, profiles, puzzle attempts, solves, and achievements.
4. Make DATABASE_URL select the backend and run migrations as a release step, not during web requests.
5. Keep an export/import path from ~/.lux/state.json for existing CLI users.

Do not treat the Compose PostgreSQL service as active application persistence until these migrations and repository changes land.