test(k8s): gate the Helm chart with a render + schema check (refs #25)

`make k8s-lint` runs `helm lint` plus a full `helm template`, so a values typo or a
malformed resource is caught without a cluster — the only automated check the chart
can have while CI has no Kubernetes to deploy into.

Red: there is no chart to lint yet.

Makefile

@@ -43,7 +43,7 @@ export DOCKER_HOST := unix://$(PODMAN_SOCK)
 endif
 endif
 
-.PHONY: ci lint build unit mutation frontend integration verify verify-up verify-acl verify-nrc verify-projection verify-bff verify-domain verify-observability verify-tracing verify-metrics verify-objecttypen verify-objecten verify-registerrecord verify-objecten-notifications verify-notifications smoke up down local verify-local local-down changelog openzaak-up openzaak-smoke openzaak-seed openzaak-down stack-up stack-smoke stack-down keycloak-up keycloak-smoke keycloak-down flowable-up flowable-smoke flowable-down help
+.PHONY: ci lint build unit mutation frontend integration verify verify-up verify-acl verify-nrc verify-projection verify-bff verify-domain verify-observability verify-tracing verify-metrics verify-objecttypen verify-objecten verify-registerrecord verify-objecten-notifications verify-notifications smoke up down local verify-local local-down changelog openzaak-up openzaak-smoke openzaak-seed openzaak-down stack-up stack-smoke stack-down keycloak-up keycloak-smoke keycloak-down flowable-up flowable-smoke flowable-down k8s-lint help
 
 ## ci: run the full pipeline — lint, build, unit, mutation, frontend, verify (mirrors Gitea Actions)
 ## `verify` is the live-stack stage (full stack up once → ACL + notification checks).
@@ -330,6 +330,26 @@ flowable-down:
 	docker compose -f $(FL_COMPOSE) down --volumes
 	-docker volume rm -f rr-fl-bpmn
 
+# ── Kubernetes (single-node Talos) ─────────────────────────────────────────────
+# The Helm chart in infra/helm/big-reference is a port of infra/docker-compose.yml
+# (ADR-0033). Full walkthrough: docs/runbooks/kubernetes-talos.md.
+#   TALOS_HOST   the address the BROWSER uses — pins Keycloak's issuer and the portals'
+#                OIDC authority. Use `localhost` with `make k8s-portals`: the OIDC
+#                library needs crypto.subtle, which browsers only expose on a secure
+#                context (https, or localhost) — see docs/runbooks/kubernetes-talos.md §5
+#   K8S_REGISTRY the registry both sides use for this repo's images (see k8s-registry)
+K8S_NS       ?= big
+K8S_CHART    := infra/helm/big-reference
+K8S_REGISTRY ?=
+TALOS_HOST   ?=
+# The images built from this repo — compose service name == image name == chart workload.
+K8S_IMAGES   := acl domain bff event-subscriber projection-api self-service openbaar behandel beheer
+
+## k8s-lint: render + schema-check the Helm chart (no cluster needed)
+k8s-lint:
+	helm lint $(K8S_CHART)
+	helm template big $(K8S_CHART) -n $(K8S_NS) --set images.registry=registry.invalid:5000 >/dev/null
+
 ## help: list available targets
 help:
 	@grep -E '^## ' $(MAKEFILE_LIST) | sed 's/^## //'