S3 module wraps aws-sdk-s3 against MinIO. Two clients on purpose:
- The bytes-mover client points at S3_ENDPOINT (internal minio:9000 over
the storage Docker network).
- The presign-only client points at S3_PUBLIC_ENDPOINT (https://s3.asxp.io
via Traefik) so the URLs it mints resolve from a browser.
force_path_style on both because subdomain-style URLs would require wildcard
DNS under s3.asxp.io.
AdminAuth is a tiny Rack middleware that 401s any request under /admin
unless HTTP Basic credentials match ADMIN_USER / ADMIN_PASSWORD from env.
Fails closed if either env var is missing.
