CD: Automate database migrations on staging deployment

[vprashrex]

Describe the current behavior
Staging deployment does not run database migrations automatically, requiring manual intervention after every migration.

Describe the enhancement you'd like
Run alembic upgrade head at CD deployment.

Why is this enhancement needed?
PR #558 deployment without auto-migration caused 80% Sentry error quota consumption. Currently, every schema change requires a developer to manually run the migration on the server.

Additional context
Verified locally using docker run to simulate ECS deployment.