Fail CI if Alembic autogenerate detects schema drift

Description
At present, we don’t have an automated way to ensure that our SQLModel data models and the database schema are in sync. The only way to check is manually, typically by running the alembic revision command. However, this step can easily be overlooked by someone pushing code, which can lead to inconsistencies accumulating over time. To automate this verification, we should add a CI step that runs:

alembic revision --autogenerate -m "ci check"

and then verifies that the generated migration file is empty (i.e., it contains no upgrade()/downgrade() operations).

If alembic generates non-empty changes, the CI job should fail, signalling a mismatch between the current database schema and our models.

Acceptance Criteria

• Add a step in GitHub Actions workflow to run alembic revision --autogenerate against the test database.

• Fail the job if the generated migration contains actual schema changes.

• Clean up the generated revision file after the check.

Localiza el workflow de GitHub Actions y la configuración existente de la base de datos de pruebas; después, revisa la configuración de Alembic utilizada por el proyecto. Ejecuta el comando autogenerate especificado contra esa base de datos y determina cómo detectar operaciones upgrade()/downgrade() no vacías. Se considera completado cuando el workflow falla ante una divergencia del esquema y elimina después la revisión generada.