cyberchef: honour ingress.enabled, add null-safe hardening

Three changes, all about values that do not do what they promise:

1. Ingress gate (#93): the Ingress template is wrapped in
   {{- if .Values.ingress.enabled }}. The key already existed in
   values.yaml with default true but was never read, so switching it off
   did nothing. Both required() calls for domain and clusterIssuer live
   inside the Ingress file, so gating also removes the contradiction that
   one had to supply a domain and issuer in order to turn off an Ingress
   one does not want.

2. Null-safety for hardening, probes and resources (#99): an override
   written without children is YAML null and erased the whole default
   sub-tree, rendering "securityContext: null" - an unhardened container
   that starts and reports healthy.

3. values.schema.json types (#68 + #99): the blocks covered by the
   null-safety accept null. This is load-bearing only for keys that have
   no chart default (e.g. resources.limits): there Helm has nothing to
   delete, so the null survives into schema validation and a strict
   "object" type rejected it outright.

Rendering with normal values is byte-identical to 7.0.0.

cyberchef/templates/NOTES.txt

@@ -1,6 +1,8 @@
 {{- $replicas := include "cyberchef.replicas" (dict "scaleDown" .Values.scaleDown "replicas" .Values.cyberchef.replicas) -}}
 CyberChef {{ .Chart.AppVersion }} — release {{ .Release.Name }} in namespace {{ .Release.Namespace }}.
 
+{{- if .Values.ingress.enabled }}
+
 ACCESS
   https://{{ .Values.ingress.domain }}
 
@@ -11,11 +13,25 @@ ACCESS
 
   This chart has no secrets and no volumes — the two ingress values above are
   everything an installation needs.
+{{- else }}
+
+ACCESS — NO INGRESS
+  ingress.enabled is false, so this release has no Ingress and no certificate;
+  ingress.domain and ingress.clusterIssuer are not needed. The app is only
+  reachable inside the cluster, as
+  {{ .Release.Name }}-{{ .Chart.Name }}-service:80. To open it locally:
+
+    kubectl -n {{ .Release.Namespace }} port-forward svc/{{ .Release.Name }}-{{ .Chart.Name }}-service 8080:80
+
+  Then browse to http://localhost:8080. Set ingress.enabled=true together with
+  ingress.domain and ingress.clusterIssuer to publish it instead.
+{{- end }}
 {{ if eq $replicas "0" }}
 SCALED TO ZERO
-  {{ if .Values.scaleDown }}scaleDown: true{{ else }}cyberchef.replicas: 0{{ end }} — the deployment runs with replicas: 0, so the URL
-  above answers 503 until you set it back and upgrade again. Service and
-  Ingress stay in place, so the certificate is not re-issued.
+  {{ if .Values.scaleDown }}scaleDown: true{{ else }}cyberchef.replicas: 0{{ end }} — the deployment runs with replicas: 0, so the endpoint
+  above does not answer until you set it back and upgrade again. Service{{ if .Values.ingress.enabled }} and
+  Ingress stay in place, so the certificate is not re-issued.{{ else }} stays in
+  place.{{ end }}
 {{ end }}
 ANYONE WHO REACHES THE URL CAN USE IT
   CyberChef has no login, and this chart adds none. If it must not be open to