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>

cert-manager/wildcard-certificate.yaml

@@ -0,0 +1,19 @@
+---
+apiVersion: cert-manager.io/v1
+kind: Certificate
+metadata:
+  name: wildcard-wild-cloud
+  namespace: cert-manager
+spec:
+  secretName: wildcard-wild-cloud-tls
+  dnsNames:
+    - "*.{{ .cloudDomain }}"
+    - "{{ .cloudDomain }}"
+  issuerRef:
+    name: letsencrypt-prod
+    kind: ClusterIssuer
+  duration: 2160h # 90 days
+  renewBefore: 360h # 15 days
+  privateKey:
+    algorithm: RSA
+    size: 2048