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>

nvidia-device-plugin/manifest.yaml

@@ -0,0 +1,9 @@
+name: nvidia-device-plugin
+is: nvidia-device-plugin
+description: NVIDIA device plugin for Kubernetes
+version: v0.17.1
+namespace: kube-system
+deploymentName: nvidia-device-plugin-daemonset
+category: infrastructure
+requires:
+  - name: node-feature-discovery