[Bug]: OCI archives without manifest descriptor annotations fail to import

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Description

OCI archives without manifest descriptor annotations fail to load with Error: internalError: "Failed to import image". Per the OCI Image Spec, these annotations are optional.

Reproduction

1. Create an OCI archive without manifest descriptor annotations (e.g., using nix2container)
2. Run container i load -i archive.tar
3. Result: Error: internalError: "Failed to import image"

Root Cause

LocalOCILayoutClient.getImageReferencefromDescriptor returns nil when annotations are missing, causing the manifest to be skipped in the import loop (ImageStore+OCILayout.swift:82-85).

Possible Solutions

1. Use archive filename for image name, then fall back to digest-based reference: "untagged@\(descriptor.digest)"
2. Add a --ref name:tag flag to container i load for specifying the image name and tag
3. Provide a clearer error message explaining annotations are required

Docker/Podman handle this by displaying untagged images as <none>:<none>.