docs: update Headlamp install namespace references from kube-system to headlamp

Updates all documentation references to the Headlamp install namespace
from kube-system to headlamp as part of PRI-433.

In-scope files updated:
- README.md, SECURITY.md
- docs/getting-started/installation.md, quick-start.md, prerequisites.md
- docs/deployment/helm.md, kubernetes.md, production.md
- docs/troubleshooting/README.md, common-issues.md, rbac-issues.md
- docs/user-guide/configuration.md, rbac-permissions.md
- docs/TESTING.md, TROUBLESHOOTING.md, DEPLOYMENT.md

Out-of-scope (unchanged):
- Source files referencing upstream workload namespace
- RBAC manifests describing Polaris namespace (polaris ns is unchanged)
- NetworkPolicy namespaceSelector (API server runs in kube-system)
- design-decisions.md and ARCHITECTURE.md (URL hashes refer to cluster namespaces, not Headlamp install ns)

Co-Authored-By: Paperclip <noreply@paperclip.ing>

docs/deployment/helm.md

@@ -41,11 +41,11 @@ pluginsManager:
 ```bash
 # Install Headlamp
 helm install headlamp headlamp/headlamp \
-  --namespace kube-system \
+  --namespace headlamp \
   --values headlamp-values.yaml
 
 # Wait for deployment
-kubectl -n kube-system wait --for=condition=available deployment/headlamp --timeout=300s
+kubectl -n headlamp wait --for=condition=available deployment/headlamp --timeout=300s
 ```
 
 After installation, install the plugin via Headlamp UI (**Settings → Plugins → Catalog**).
@@ -131,7 +131,7 @@ Deploy:
 
 ```bash
 helm upgrade --install headlamp headlamp/headlamp \
-  --namespace kube-system \
+  --namespace headlamp \
   --values headlamp-values.yaml \
   --wait \
   --timeout 5m
@@ -177,7 +177,7 @@ apiVersion: v1
 kind: ConfigMap
 metadata:
   name: headlamp-plugin-config
-  namespace: kube-system
+  namespace: headlamp
 data:
   plugin.yml: |
     - name: headlamp-polaris-plugin
@@ -191,7 +191,7 @@ Apply ConfigMap then deploy Headlamp:
 kubectl apply -f headlamp-plugin-config.yaml
 
 helm upgrade --install headlamp headlamp/headlamp \
-  --namespace kube-system \
+  --namespace headlamp \
   --values headlamp-values.yaml
 ```
 
@@ -221,7 +221,7 @@ apiVersion: helm.toolkit.fluxcd.io/v2
 kind: HelmRelease
 metadata:
   name: headlamp
-  namespace: kube-system
+  namespace: headlamp
 spec:
   interval: 30m
   chart:
@@ -300,7 +300,7 @@ kubectl apply -f helmrepository.yaml
 kubectl apply -f helmrelease.yaml
 
 # Watch deployment
-flux get helmreleases -n kube-system --watch
+flux get helmreleases -n headlamp --watch
 ```
 
 ## RBAC Configuration
@@ -329,7 +329,7 @@ metadata:
 subjects:
   - kind: ServiceAccount
     name: headlamp
-    namespace: kube-system
+namespace: headlamp
 roleRef:
   kind: Role
   name: polaris-proxy-reader
@@ -349,7 +349,7 @@ helm repo update
 
 # Upgrade Headlamp (preserves plugin configuration)
 helm upgrade headlamp headlamp/headlamp \
-  --namespace kube-system \
+  --namespace headlamp \
   --values headlamp-values.yaml \
   --wait
 ```
@@ -365,15 +365,15 @@ helm upgrade headlamp headlamp/headlamp \
 
 ```bash
 # Update ConfigMap with new version
-kubectl -n kube-system edit configmap headlamp-plugin-config
+kubectl -n headlamp edit configmap headlamp-plugin-config
 
 # Update version and URL:
 # version: 0.3.6
 # url: https://github.com/.../v0.3.6/polaris-0.3.10.tar.gz
 
 # Restart deployment to trigger init container
-kubectl -n kube-system rollout restart deployment/headlamp
-kubectl -n kube-system rollout status deployment/headlamp
+kubectl -n headlamp rollout restart deployment/headlamp
+kubectl -n headlamp rollout status deployment/headlamp
 ```
 
 ## Troubleshooting
@@ -382,25 +382,25 @@ kubectl -n kube-system rollout status deployment/headlamp
 
 ```bash
 # Check Headlamp values
-helm get values headlamp -n kube-system
+helm get values headlamp -n headlamp
 
 # Verify plugin files exist
-kubectl -n kube-system exec deployment/headlamp -c headlamp -- \
+kubectl -n headlamp exec deployment/headlamp -c headlamp -- \
   ls -la /headlamp/plugins/headlamp-polaris-plugin/
 
 # If missing, reinstall plugin via UI or check init container logs
-kubectl -n kube-system logs deployment/headlamp -c install-polaris-plugin
+kubectl -n headlamp logs deployment/headlamp -c install-polaris-plugin
 ```
 
 ### Helm Release Stuck
 
 ```bash
 # Check Helm release status
-helm list -n kube-system
+helm list -n headlamp
 
 # If stuck, force upgrade
 helm upgrade headlamp headlamp/headlamp \
-  --namespace kube-system \
+  --namespace headlamp \
   --values headlamp-values.yaml \
   --force \
   --wait
@@ -410,13 +410,13 @@ helm upgrade headlamp headlamp/headlamp \
 
 ```bash
 # Check HelmRelease status
-flux get helmreleases -n kube-system
+flux get helmreleases -n headlamp
 
 # Check events
-kubectl -n kube-system describe helmrelease headlamp
+kubectl -n headlamp describe helmrelease headlamp
 
 # Force reconciliation
-flux reconcile helmrelease headlamp -n kube-system
+flux reconcile helmrelease headlamp -n headlamp
 ```
 
 ## Next Steps