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>

charts/envoy-gateway/templates/envoy-gateway-config.yaml

@@ -0,0 +1,15 @@
+apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: envoy-gateway-config
+  namespace: '{{ .Release.Namespace }}'
+  labels:
+  {{- include "eg.labels" . | nindent 4 }}
+data:
+  envoy-gateway.yaml: |
+    apiVersion: gateway.envoyproxy.io/v1alpha1
+    kind: EnvoyGateway
+    {{- $baseEnvoyGatewayConfig := include "eg.default-envoy-gateway-config" . | fromYaml }}
+    {{- $userEnvoyGatewayConfig := .Values.config.envoyGateway }}
+    {{- $mergedEnvoyGatewayConfig := merge $userEnvoyGatewayConfig $baseEnvoyGatewayConfig }}
+    {{- toYaml $mergedEnvoyGatewayConfig | nindent 4 }}