Makefile: add build-update-image target for update testing

Move the update image build logic out of e2e test code and into a
Makefile target. Build the update image as part of deploy-bink so it
is available for both manual testing and e2e tests.

Assisted-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: alicefr

Makefile

@@ -85,6 +85,12 @@ build-daemon: ## Build daemon binary.
 buildimg: ## Build container image.
 	$(CONTAINER_TOOL) build -t $(IMG) .
 
+.PHONY: build-update-image
+build-update-image: ## Build a derived node image for update testing and push to bink registry.
+	@printf 'FROM localhost:5000/node:latest\nRUN touch /usr/share/update-marker\n' | \
+		podman build -t localhost:5000/node:update -f - .
+	podman push --tls-verify=false localhost:5000/node:update
+
 ##@ Deployment
 
 ifndef ignore-not-found
@@ -135,6 +141,7 @@ start-bink: seed-node-image ## Start a bink cluster (idempotent).
 
 .PHONY: deploy-bink
 deploy-bink: start-bink kustomize ## Deploy to a bink cluster (requires: buildimg).
+	$(MAKE) build-update-image
 	podman push --tls-verify=false $(IMG) localhost:5000/bootc-operator-e2e:latest
 	@existed=$$(kubectl --kubeconfig $(KUBECONFIG_BINK) -n bootc-operator get deploy bootc-operator-controller-manager -o name 2>/dev/null || true) && \
 	$(MAKE) deploy KUBECONFIG=$(abspath $(KUBECONFIG_BINK)) IMG=$(IMG_BINK) && \