Correct the fix: mark the namespace prune-disabled, don't drop it from inventory

Dropping it from resources: was the same accident by a different door — Flux
prunes anything that disappears from a Kustomization's rendered inventory, so
the live Kustomization's next reconcile would have deleted the namespace
itself. Caught before it fired by suspending that Kustomization.

kustomize.toolkit.fluxcd.io/prune: disabled on the object is the documented
way to keep Flux creating/updating a resource while never deleting it.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

k8s/kustomization.yaml

@@ -1,6 +1,7 @@
 apiVersion: kustomize.config.k8s.io/v1beta1
 kind: Kustomization
 resources:
+  - namespace.yaml
   - ca-configmap.yaml
   - externalsecret.yaml
   - configmap.yaml