Add Helm-based ArgoCD Applications for platform operators

- Longhorn: Helm chart v1.7.2 (sync-wave -2, installs first)
- cert-manager: Helm chart v1.16.3 with CRDs enabled
- CloudNativePG: Helm chart v0.23.0
- Sealed Secrets: Helm chart v2.16.2
- Remove custom StorageClass (Helm chart manages it)

Previously only config resources were deployed without the actual
operators, causing PVCs to pend and CRDs to be missing.

infra/kubernetes/platform/cert-manager/kustomization.yaml

@@ -1,5 +1,6 @@
 apiVersion: kustomize.config.k8s.io/v1beta1
 kind: Kustomization
 resources:
+  - application.yaml
   - namespace.yaml
   - clusterissuer-letsencrypt.yaml