Keep simulator API error bodies through Ingress instead of branded HTML.

Disable ingress-nginx intercept for 404/405 on all lab Ingresses and document
how to verify JSON/XML responses after upgrade.

README.md

@@ -141,6 +141,13 @@ helm upgrade --install simulators charts/api-simulators-lab \
      ClusterIssuers from the chart; otherwise an existing `letsencrypt-prod` is used.
    - Let's Encrypt HTTP-01 needs **public DNS** pointing at the Ingress controller
      (not `*.lab.local`).
+   - Each Ingress sets `proxy-intercept-errors: "false"` and
+     `custom-http-errors: "502,503"` so cluster-wide branded HTML (e.g. «DevOps спит»)
+     does not replace simulator JSON/XML for 404/405/401. Do **not** put 404/405 in
+     `custom-http-errors`. After `helm upgrade`, check with
+     `curl -sH 'Accept: application/json' https://<host>/…` — expect API error body,
+     not HTML. If HTML persists, fix controller-level `custom-http-errors` on
+     ingress-nginx (outside this chart).
 
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