Remove nessus app and fix envoy-gateway OCI chart bug

- Delete nessus Application CRD, manifests, and bootstrap script
- Vendor envoy-gateway Helm chart (v1.6.3) locally to work around
  ArgoCD v3.3.3 Docker Hub OCI resolution bug
- Re-enable auto-sync for envoy-gateway

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

argocd-apps/apps/nessus.yaml

@@ -1,30 +0,0 @@
-apiVersion: argoproj.io/v1alpha1
-kind: Application
-metadata:
-  name: nessus
-  namespace: argocd
-  annotations:
-    argocd.argoproj.io/sync-wave: "51"
-  finalizers:
-    - resources-finalizer.argocd.argoproj.io
-spec:
-  project: applications
-  source:
-    repoURL: https://gitlab.kube.huskypup.net/Scooby/Homelabv4.git
-    targetRevision: main
-    path: apps/nessus/manifests
-  destination:
-    server: https://kubernetes.default.svc
-    namespace: nessus
-  syncPolicy:
-    automated:
-      prune: true
-      selfHeal: true
-    managedNamespaceMetadata:
-      labels:
-        pod-security.kubernetes.io/enforce: privileged
-    syncOptions:
-      - CreateNamespace=true
-      - ServerSideApply=true
-      - ServerSideDiff=true
-      - RespectIgnoreDifferences=true