feature: join k3s-worker-3 into the cluster

Wires the k8s-bootstrap join sequence (start, SSH wait, k3s agent join,
Longhorn disk mount) and the k8s-infra Longhorn disk patch for worker-3.
Its VM was already provisioned by proxmox-infra in an earlier branch.

03-k8s-infra/index.ts

@@ -143,7 +143,7 @@ const longhorn = new k8s.helm.v3.Release(
 );
 
 // Patches Longhorn instances to use the mountend Longhorn storage on the worker nodes.
-["k3s-worker-1", "k3s-worker-2"].forEach(
+["k3s-worker-1", "k3s-worker-2", "k3s-worker-3"].forEach(
   (nodeName) =>
     new k8s.apiextensions.CustomResourcePatch(
       `${nodeName}-longhorn-disks`,