**Updated Original PR Description**
## Summary
This PR adds a small, controlled set of scheduling fields to WorkerPool
so WorkerPool-managed Pods can be placed onto appropriate Kubernetes
nodes.
Added fields:
- `nodeSelector`
- `tolerations`
- `priorityClassName`
- `nodeAffinity`
## Scope
This intentionally does not expose a full `PodTemplateSpec`, and does
not add support for full `affinity`, `podAffinity`, or
`podAntiAffinity`.
Resource requests/limits are intentionally left out of scope for this CL
while the WorkerPool resource model is still being discussed separately.
The goal is to keep the first version small while addressing the
WorkerPool-to-Kubernetes-Node scheduling gap discussed in
[#212](https://github.com/agent-substrate/substrate/issues/212).
`nodeAffinity` is included to support heterogeneous node pools where
`nodeSelector` is too limited, such as requiring or preferring one of
several equivalent accelerator/local-SSD/cache node pools, or expressing
soft preferences during node pool migration.
`priorityClassName` is included to help preserve warm WorkerPool
capacity under cluster pressure. Since WorkerPool pods are the slots
available for actor resume, higher-priority pools can protect
latency-sensitive or interactive actor workloads from displacement by
lower-priority batch workloads, and allow different WorkerPools to
represent different service classes, e.g. interactive vs. batch.
## Related issue
Part of #212.
Related to #47.
