Document runtime compatibility for mounting ModelPack artifacts

[raravena80]

This came up in the #modelpack Slack thread with the Zarf folks (airgap packaging). Is there a documented runtime compatibility matrix? Right now the answer is no. The getting-started guide only mentions CRI-O.

This was tracked in #33, but the stale bot closed it. Current upstream status:

• CRI-O: artifact mounts shipped (OCI Artifact Mounts cri-o/cri-o#8953, closed 2025-04-30)
• containerd: open (Mount OCI Artifacts containerd/containerd#11381)
• moby: open (Mount OCI Artifacts moby/moby#49591)

Kubernetes image volumes (KEP-4639) are GA as of 1.36, so users will expect image: volumes to just work with ModelPack artifacts. With raw, non-tar layers that only holds on CRI-O today.

Proposal:

1. Add a compatibility page to the docs: runtime, minimum version, image volume support for ModelPack artifacts, and notes. It should also cover the model CSI driver as the runtime-independent path.
2. Keep this issue open, and exempt it from the stale bot, until containerd and moby land support.