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.

GitHub Actions の workflow と既存のテストデータベースのセットアップを確認し、その後、プロジェクトで使用されている Alembic の設定を調べてください。そのデータベースに対して指定された autogenerate コマンドを実行し、空でない upgrade()/downgrade() 操作を検出する方法を決定してください。workflow がスキーマドリフトで失敗し、その後に生成された revision を削除すれば完了です。