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

Updates documentation to reflect that Headlamp is installed in the
'headlamp' namespace (not 'kube-system'). Only documentation files
that reference the Headlamp install namespace are changed.

Changed files:
- docs/deployment/production.md: NetworkPolicy namespaceSelector
- docs/troubleshooting/network-problems.md: NetworkPolicy namespaceSelector
- docs/user-guide/rbac-permissions.md: NetworkPolicy namespaceSelector
- e2e/README.md: kubectl commands for local E2E testing

Files NOT changed (upstream workload namespace - out of scope per PRI-340):
- Source files, tests, or configs referencing where Polaris runs

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

docs/deployment/production.md

@@ -160,7 +160,7 @@ spec:
     - from:
         - namespaceSelector:
             matchLabels:
-              kubernetes.io/metadata.name: kube-system
+              kubernetes.io/metadata.name: headlamp
         - podSelector:
             matchLabels:
               component: kube-apiserver

docs/troubleshooting/network-problems.md

@@ -41,7 +41,7 @@ spec:
     - from:
         - namespaceSelector:
             matchLabels:
-              kubernetes.io/metadata.name: kube-system
+              kubernetes.io/metadata.name: headlamp
         - podSelector:
             matchLabels:
               component: kube-apiserver

docs/user-guide/rbac-permissions.md

@@ -318,7 +318,7 @@ spec:
     - from:
         - namespaceSelector:
             matchLabels:
-              kubernetes.io/metadata.name: kube-system
+              kubernetes.io/metadata.name: headlamp
         - podSelector:
             matchLabels:
               component: kube-apiserver

e2e/README.md

@@ -41,8 +41,8 @@ The default base URL is `https://headlamp.animaniacs.farh.net`. Override with `H
 ### Option 2: K8s bearer token (port-forward)
 
 ```bash
-kubectl port-forward -n kube-system svc/headlamp 4466:80
-export HEADLAMP_TOKEN=$(kubectl create token headlamp -n kube-system)
+kubectl port-forward -n headlamp svc/headlamp 4466:80
+export HEADLAMP_TOKEN=$(kubectl create token headlamp -n headlamp)
 HEADLAMP_URL=http://localhost:4466 npm run e2e
 ```
 
@@ -143,7 +143,7 @@ cp .env.example .env
 
 # 3. Set environment variables
 export HEADLAMP_URL=https://your-headlamp-instance.com
-export HEADLAMP_TOKEN=$(kubectl create token headlamp -n kube-system)
+export HEADLAMP_TOKEN=$(kubectl create token headlamp -n headlamp)
 
 # 4. Run tests
 npm run e2e