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>

gitea/manifest.yaml

@@ -5,6 +5,7 @@ version: 1.24.3
 icon: https://cdn.jsdelivr.net/gh/homarr-labs/dashboard-icons/svg/gitea.svg
 requires:
 - name: postgres
+- name: smtp
 defaultConfig:
   namespace: gitea
   externalDnsDomain: '{{ .cloud.domain }}'
@@ -24,10 +25,10 @@ defaultConfig:
   timezone: UTC
   runMode: prod
   smtp:
-    host: '{{ .cloud.smtp.host }}'
-    port: '{{ .cloud.smtp.port }}'
-    user: '{{ .cloud.smtp.user }}'
-    from: '{{ .cloud.smtp.from }}'
+    host: '{{ .apps.smtp.host }}'
+    port: '{{ .apps.smtp.port }}'
+    user: '{{ .apps.smtp.user }}'
+    from: '{{ .apps.smtp.from }}'
 defaultSecrets:
 - key: adminPassword
 - key: dbPassword