Updates MinIO credentials to meet minimum length requirements:
- MINIO_ROOT_USER: at least 3 characters (was 'minioadmin')
- MINIO_ROOT_PASSWORD: at least 8 characters (was 'minioadmin')
Now uses environment variables with sensible defaults that can be
overridden via .env file or GitHub Actions secrets.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
