[Task] Document a MinIO or S3-compatible data-handoff example

[ryan-wong-coder]

Background\n\nA common TrustDB workflow is proving which file or report was delivered to another party while keeping content in existing object storage.\n\n## Scope\n\nWrite a reproducible example showing an object downloaded from an S3-compatible service, proved with TrustDB, and verified after delivery. MinIO may be used for the local demonstration.\n\n## Acceptance criteria\n\n- Uses Docker or another reproducible local setup.\n- Does not claim that TrustDB stores or protects the original object.\n- Shows which object metadata is signed and which is merely descriptive.\n- Includes successful verification and a modified-object failure.\n- Keeps credentials and generated keys disposable.