feat(k8s): Helm chart for the whole stack on a single-node cluster (refs #25)

One chart whose values.yaml is a near-literal transcription of
infra/docker-compose.yml, rendered by three generic templates (Deployment, Job,
Service) over a `workloads` map — so the two stacks can be diffed by eye instead
of by archaeology, and adding a service is a values edit.

Platform-forced deviations, each commented where it appears:
- `args`, never `command`: compose replaces the image CMD, Kubernetes replaces the
  ENTRYPOINT. The chart fails to render on `command`, because the symptom (postgres
  refusing to run as root, Keycloak exec-ing `start-dev`) is nothing like the cause.
- The four Django services apply their own setup_configuration in the web pod
  rather than in a separate init Job: both scripts migrate, and without compose's
  depends_on they race the same database.
- OpenZaak and Objecten are addressed by service FQDN, because Django rejects a
  single-label host in a URL — the reason compose passes container IPs around.
- NodePorts, no ingress; databases are emptyDir until persistence.storageClass is
  set, so the stack comes up on a cluster with no CSI driver.

The upstream config inputs stay in the repo and become ConfigMaps via
infra/helm/seed-configmaps.sh — the Kubernetes sibling of infra/seed-config.sh —
so the compose stack and the chart cannot fork. infra/helm/registry.yaml runs an
in-cluster registry because Talos cannot side-load an image and a laptop-side one
needs a root-level firewall change.

infra/helm/seed-configmaps.sh

@@ -0,0 +1,46 @@
+#!/usr/bin/env bash
+#
+# Turn the repo's config inputs into the ConfigMaps the Helm chart mounts.
+#
+# This is the Kubernetes sibling of infra/seed-config.sh: the upstream Common
+# Ground images are used verbatim and read their config from a mounted directory,
+# so the config has to be handed to the platform out-of-band. Compose gets it via
+# `docker cp` into external volumes; Kubernetes gets it as ConfigMaps created from
+# the files that already live in this repo. Copying those files into the chart
+# would fork them from the compose stack, so we don't.
+#
+# Idempotent: re-run after editing any data.yaml, then `make k8s-reseed`.
+#
+# Usage: seed-configmaps.sh [namespace]      (default: big)
+set -euo pipefail
+
+ns="${1:-big}"
+here="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+repo="$(cd "$here/../.." && pwd)"
+
+kubectl get namespace "$ns" >/dev/null 2>&1 || kubectl create namespace "$ns"
+
+seed() {  # name  <kubectl --from-file args...>
+  local name="$1"; shift
+  kubectl create configmap "$name" -n "$ns" "$@" \
+    --dry-run=client -o yaml | kubectl apply -f - >/dev/null
+  echo "  seeded configmap/$name"
+}
+
+seed rr-oz-config            --from-file="$repo/infra/openzaak/setup_configuration/"
+seed rr-nrc-config           --from-file="$repo/infra/opennotificaties/setup_configuration/"
+seed rr-kc-realms            --from-file="$repo/infra/keycloak/realms/"
+seed rr-objecttypen-config   --from-file="$repo/infra/objecttypen/setup_configuration/"
+seed rr-objecten-config      --from-file="$repo/infra/objecten/setup_configuration/"
+# register.py + the RegisterRecord JSON schema (the __pycache__ dir is skipped:
+# kubectl only takes regular files from a --from-file directory).
+seed rr-registerrecord-config --from-file="$repo/infra/objecttypen-registerrecord/"
+# The BPMN and the DMN are two separate Flowable deployments (S-13, ADR-0016).
+seed rr-fl-bpmn \
+  --from-file="$repo/workflows/registratie.bpmn" \
+  --from-file="$repo/workflows/diploma-eligibility.dmn"
+# The two bootstrap scripts the compose local stack runs as init containers
+# (S-B04, ADR-0020). Stdlib-only, so a plain python image can run them.
+seed rr-seed-scripts \
+  --from-file="$repo/infra/openzaak/seed_catalogus.py" \
+  --from-file="$repo/infra/local/register-abonnement.py"