CRI pod sandboxes

A pod sandbox is a verified OCI pause workload owned by the CRI plugin and executed by Stackied. The plugin preserves kubelet metadata, labels, annotations, namespace choices, DNS, port mappings, Linux security context, cgroup resources, sysctls, user-namespace mappings, and log ownership in one typed admission request. CNI attachment must finish before creation reports success; failed creation rolls back partial workload and network state.

Repeating create with the same pod identity returns the same sandbox ID. Stop and remove are idempotent. Status, list, and streaming list return the original metadata and exact ready/not-ready and network state.