docs: fix observerURL browser-reachability guidance (#688)

- namespace-management: replace svc.cluster.local example with a
  placeholder and add a note explaining browser-reachability and CORS
- multi-cluster-connectivity: correct the reachability note and add
  a CORS callout in the Register Observability Plane section
- multi-cluster-connectivity: add a note that the Helm command shows
  only Cluster Agent flags; full observer config (gateway, OIDC, CORS)
  should be taken from the On Your Environment guide

Signed-off-by: Rashad Sirajudeen <rashad@wso2.com>

Author: rashadism

docs/platform-engineer-guide/multi-cluster-connectivity.mdx

@@ -375,7 +375,7 @@ EOF
 
 ### Register an Observability Plane
 
-The `observerURL` must be reachable from the Control Plane cluster. In multi-cluster setups this cannot be an in-cluster `svc.cluster.local` address. Use the Observability Plane's external gateway URL or a routable DNS name instead.
+The `observerURL` must be reachable from the **user's browser** — the portal fetches telemetry directly from the Observer. Use the Observability Plane's external gateway URL and ensure `cors.allowedOrigins` includes the portal origin (e.g. `https://console.${DOMAIN}`) — see the [On Your Environment](../getting-started/try-it-out/on-your-environment.mdx) guide for the full gateway and CORS configuration.
 
 ```bash
 AGENT_CA=$(kubectl --context $REMOTE_CONTEXT get secret cluster-agent-tls \

docs/platform-engineer-guide/namespace-management.mdx

@@ -328,11 +328,15 @@ spec:
       clientCA:
         value: |
 $(echo "$OP_CA_CERT" | sed 's/^/ /')
-observerURL: http://observer.openchoreo-observability-plane.svc.cluster.local:8080
+observerURL: https://observer.<your-obs-domain>
 EOF`}
 
 </CodeBlock>
 
+:::note
+`observerURL` must be a browser-reachable HTTPS URL — the portal fetches telemetry directly from the Observer. Use the Observer's gateway-exposed hostname and ensure `observer.cors.allowedOrigins` includes the portal origin. See [On Your Environment](../getting-started/try-it-out/on-your-environment.mdx) for example gateway and CORS configuration.
+:::
+
 **Verification:**
 
 <CodeBlock language="bash">