serves.s3-bucket.region still said us-east-1 (PR #58 already fixed this,
unmerged) while the live mesh-minio sidecar had MESH_MINIO_REGION=eu-west
set out-of-band, not in the manifest at all — and the actual minio server
had no region configured whatsoever (mc admin config get region: empty),
apparently lost across a container recreation since nothing declared it.
Every s3-bucket consumer binding ${bound:s3-bucket:region} was reading
the stale us-east-1 declaration regardless of what was actually live.
Declares MINIO_REGION on the server container and MESH_MINIO_REGION on
the sidecar, matching the static serves declaration, so this is mesh-
managed and durable rather than a manual mc admin config or docker env
override that the next recreation silently drops.