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>

mastodon/manifest.yaml

@@ -6,6 +6,7 @@ icon: https://cdn.jsdelivr.net/gh/homarr-labs/dashboard-icons/svg/mastodon.svg
 requires:
   - name: postgres
   - name: redis
+  - name: smtp
 defaultConfig:
   namespace: mastodon
   externalDnsDomain: "{{ .cloud.domain }}"
@@ -31,14 +32,14 @@ defaultConfig:
   systemStorage: 100Gi
   # SMTP configuration
   smtp:
-    enabled: "{{ .cloud.smtp.host | ternary true false }}"
-    server: "{{ .cloud.smtp.host }}"
-    port: "{{ .cloud.smtp.port }}"
+    enabled: "{{ .apps.smtp.host | ternary true false }}"
+    server: "{{ .apps.smtp.host }}"
+    port: "{{ .apps.smtp.port }}"
     from: notifications@{{ .cloud.domain }}
-    user: "{{ .cloud.smtp.user }}"
+    user: "{{ .apps.smtp.user }}"
     authMethod: plain
     enableStarttls: auto
-    tls: "{{ .cloud.smtp.tls }}"
+    tls: "{{ .apps.smtp.tls }}"
   # TLS
   tlsSecretName: wildcard-wild-cloud-tls
   # Sidekiq configuration