fix(pihole): add nodeSelector + dnsPolicy to prevent volume conflicts

- nodeSelector: rnk-wrk01 prevents RWO Multi-Attach on rollout
- dnsPolicy: None + external nameservers prevents DNS loop in pod

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

k8s/pihole/deployment.yaml

@@ -15,6 +15,13 @@ spec:
       labels:
         app: pihole
     spec:
+      nodeSelector:
+        kubernetes.io/hostname: rnk-wrk01
+      dnsPolicy: None
+      dnsConfig:
+        nameservers:
+          - 1.1.1.1
+          - 8.8.8.8
       containers:
         - name: pihole
           image: pihole/pihole:latest