fix(ci): switch MinIO tests to Chainguard images (#4985)

## Summary

Switches the MinIO test and local development containers to Chainguard's
maintained Docker Hub images because the previous Quay images are no
longer publicly pullable.

## Fix

Pins the multi-platform server and client images by digest. The local
stack now uses the Chainguard client entrypoint for bucket
initialization, while test containers keep client state in a writable
temporary directory.