Rename default overlay to single-cluster

"default" is a kubebuilder convention that doesn't say what it actually
deploys. "single-cluster" describes the install topology and pairs
naturally with the cross-cluster overlay planned as a follow-up.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: scotwells

Makefile

@@ -131,7 +131,7 @@ docker-buildx: ## Build and push docker image for the manager for cross-platform
 build-installer: manifests generate kustomize ## Generate a consolidated YAML with CRDs and deployment.
 	mkdir -p dist
 	cd config/base/manager && $(KUSTOMIZE) edit set image controller=${IMG}
-	$(KUSTOMIZE) build config/overlays/default > dist/install.yaml
+	$(KUSTOMIZE) build config/overlays/single-cluster > dist/install.yaml
 
 ##@ Deployment
 
@@ -150,11 +150,11 @@ uninstall: manifests kustomize ## Uninstall CRDs from the K8s cluster specified
 .PHONY: deploy
 deploy: manifests kustomize ## Deploy controller to the K8s cluster specified in ~/.kube/config.
 	cd config/base/manager && $(KUSTOMIZE) edit set image controller=${IMG}
-	$(KUSTOMIZE) build config/overlays/default | $(KUBECTL) apply -f -
+	$(KUSTOMIZE) build config/overlays/single-cluster | $(KUBECTL) apply -f -
 
 .PHONY: undeploy
 undeploy: kustomize ## Undeploy controller from the K8s cluster specified in ~/.kube/config. Call with ignore-not-found=true to ignore resource not found errors during deletion.
-	$(KUSTOMIZE) build config/overlays/default | $(KUBECTL) delete --ignore-not-found=$(ignore-not-found) -f -
+	$(KUSTOMIZE) build config/overlays/single-cluster | $(KUBECTL) delete --ignore-not-found=$(ignore-not-found) -f -
 
 ##@ Dependencies