chore(k8s): drop backfill nodeSelector/toleration, free talos4

podAntiAffinity on app=prop already keeps the backfill pod on its own
physical host, so the dedicated nodeSelector + taint were redundant.
Removing them lets talos4 be used as a normal worker for anything else
the cluster wants to place there. The live taint and label on talos4
were cleared alongside this commit.

k8s/deployment-backfill.yaml

@@ -4,9 +4,11 @@ metadata:
   name: prop-backfill
   namespace: prop
 spec:
-  # Start with 1. Scale up as additional prop-backfill=true nodes come online
-  # (podAntiAffinity keys on physical-host, same as prop, so replicas stay
-  # spread across distinct physical hosts).
+  # Single replica. podAntiAffinity on app=prop / physical-host means
+  # this pod lands on whichever physical host the hot replicas aren't on
+  # (currently talos4 / node4); no nodeSelector or taint is needed to
+  # pin it — the antiaffinity is sufficient and keeps talos4 available
+  # as a normal scheduling target for the rest of the cluster.
   replicas: 1
   minReadySeconds: 5
   strategy:
@@ -27,15 +29,6 @@ spec:
         app: prop
         tier: backfill
     spec:
-      nodeSelector:
-        prop-backfill: "true"
-      tolerations:
-        # Matches the taint recommended for prop-backfill=true nodes. Remove
-        # this block if you haven't tainted the nodes.
-        - key: workload
-          operator: Equal
-          value: backfill
-          effect: NoSchedule
       affinity:
         podAntiAffinity:
           requiredDuringSchedulingIgnoredDuringExecution: