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>

longhorn/manifest.yaml

@@ -0,0 +1,13 @@
+name: longhorn
+is: longhorn
+description: Cloud-native distributed block storage for Kubernetes
+version: v1.8.1
+namespace: longhorn-system
+deploymentName: longhorn-ui
+category: infrastructure
+requires:
+  - name: traefik
+  - name: nfs
+defaultConfig:
+  internalDomain: "{{ .cloud.internalDomain }}"
+  backupTarget: "nfs://{{ .apps.nfs.host }}:/data/{{ .cluster.name }}/backups"