[Bug]: Error: missing required header Docker-Content-Digest on container i pull from other servers.

### I have done the following

- [x] I have searched the existing issues
- [x] If possible, I've reproduced the issue using the 'main' branch of this project

### Steps to reproduce

- register in other than docker registry where is no Docker-Container-Digest header
- try to pull image from it

### Problem description

Hello,
I got problems with pull image from other registry, even so I registered already on it.
Why `container i pull` want only one registry header? `Docker-Content-Digest`

### Environment

```markdown
- OS: 26.4.1 (25E253)
- Xcode: 26.4 (17E192)
- Container: 0.11.0 (build: release, commit: d9b8a8d)
```

### Code of Conduct

- [x] I agree to follow this project's Code of Conduct

Start by reproducing `container i pull` against a non-Docker registry that omits the `Docker-Content-Digest` header, using the reported Container 0.11.0 environment as a reference. Trace the image-pull request handling and verify the pull succeeds for registries without that header; add or update a focused regression test if the existing test suite has coverage for registry pulls.

Written by the indexing model from the issue text.