Scaffold kea-operator: CRDs, controllers, config rendering, REST API, CI

Replace the ISC dhcpd PXE-boot VM with a Kea DHCP Kubernetes operator, modelled
on bind-operator. The operator renders kea-dhcp4 config from CRs and runs an HA
pair of kea-dhcp4 + kea-ctrl-agent servers behind an anycast Service.

- add KeaCluster/KeaSubnet/KeaClientClass/KeaAPI CRDs (group kea.unkin.net)
- render deterministic kea-dhcp4.conf + kea-ctrl-agent.conf into a ConfigMap and
  roll the StatefulSet via a config-hash annotation; best-effort hot-reload via
  the kea-ctrl-agent REST channel
- run HA hot-standby (memfile leases) with stable per-peer DNS identity from a
  StatefulSet; expose an anycast LoadBalancer Service for PureLB
- represent the full legacy dhcpd config: 198.18.13-17.0/24 pools, pool-less
  198.18.25.0/24, and the Legacy/UEFI-64 PXE arch classes (option 93)
- add the KeaAPI-spawned REST service: Terraform-friendly CRUD over subnet and
  client-class CRs (stable IDs, PUT upsert, 404 drift, bearer-token auth)
- add Makefile (patch/minor/major tag targets), distroless operator/api images,
  an AlmaLinux+EPEL kea workload image, and woodpecker CI with k8s resources +
  serviceAccountName on every step
- unit tests for config rendering, controller reconcile/config-hash, and the API

Claude-Session: https://claude.ai/code/session_01JUoARVdmhxKQHyyyp1pxeT

config/samples/02-clientclasses.yaml

@@ -0,0 +1,21 @@
+# PXE boot classes matching the client architecture option (code 93), replacing
+# the legacy dhcpd "Legacy" and "UEFI-64" classes.
+apiVersion: kea.unkin.net/v1alpha1
+kind: KeaClientClass
+metadata:
+  name: Legacy
+  namespace: dhcp-system
+spec:
+  clusterRef: pxe
+  archHex: ["0x0000"]
+  bootFileName: /undionly.kpxe
+---
+apiVersion: kea.unkin.net/v1alpha1
+kind: KeaClientClass
+metadata:
+  name: UEFI-64
+  namespace: dhcp-system
+spec:
+  clusterRef: pxe
+  archHex: ["0x0007", "0x0009"]
+  bootFileName: /ipxe.efi