MinIO's community edition has been trimming features and its licensing
direction has grown less predictable. Garage (AGPL, purpose-built for
self-hosting) is a drop-in S3-compatible replacement — no changes needed
to backend/app/minio_client.py, which talks to the S3 API generically.
Deployed independently from the app stack (storage/docker-compose.yml),
same separation MinIO had. Single-node config (replication_factor = 1)
matching this project's learning/small-team scope. init-garage.sh handles
the one-time layout assignment + bucket creation Garage requires that
MinIO didn't (MinIO auto-creates buckets via API; Garage needs an
explicit `garage bucket create` step).
