Adds a compose overlay (MinIO as S3 stand-in + Mailpit as SMTP catcher,
with auto bucket creation) and a runbook so reviewers can verify the
async Excel export end-to-end locally: UI button -> Celery worker ->
S3 upload -> emailed pre-signed link -> downloadable .xlsx.
Runs under a distinct compose project name with conflicting host port
bindings reset, so it coexists with other local superset stacks.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
