feat: Move cluster services to wild-directory as unified packages

Convert all 15 cluster services from embedded API format to
wild-directory packages using the unified manifest format:
- metallb, traefik, cert-manager, longhorn, snapshot-controller
- nfs, smtp, coredns, node-feature-discovery, nvidia-device-plugin
- externaldns, docker-registry, headlamp, crowdsec, utils

Changes:
- wild-manifest.yaml → manifest.yaml with is, defaultConfig, requires
- Eliminated configReferences and serviceConfig fields
- Flattened kustomize.template/ to package root
- Template vars use flat defaultConfig keys
- install.sh paths updated for apps/ layout
- Updated 9 app manifests: cloud.smtp.* → apps.smtp.* with requires
- Removed dead install: true field from 6 app manifests

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

metallb/configuration/kustomization.yaml

@@ -0,0 +1,3 @@
+namespace: metallb-system
+resources:
+  - pool.yaml

metallb/configuration/pool.yaml

@@ -0,0 +1,19 @@
+---
+apiVersion: metallb.io/v1beta1
+kind: IPAddressPool
+metadata:
+  name: first-pool
+  namespace: metallb-system
+spec:
+  addresses:
+  - {{ .ipAddressPool }}
+
+---
+apiVersion: metallb.io/v1beta1
+kind: L2Advertisement
+metadata:
+  name: l2-advertisement
+  namespace: metallb-system
+spec:
+  ipAddressPools:
+  - first-pool