docs: replace hardcoded namespace with <your-namespace> placeholder

* 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>

* fix: correct RBAC manifest per QA review (PRI-555)

- Remove rbac.authorization.k8s.io privilege escalation block
- Fix orphaned comment from round 1
- Add EOF newline
- Keep serviceaccounts/token for E2E auth (confirmed needed)
- Namespace already correct (privilegedescalation-dev)

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

* docs: replace hardcoded namespace with <your-namespace> placeholder

Users choose their own namespace for Headlamp. Replace all hardcoded
namespace references (headlamp, kube-system) in user-facing docs with
<your-namespace> so users substitute their own value.

Conventions:
- Helm install: --namespace <your-namespace> --create-namespace
- kubectl commands: -n <your-namespace>
- YAML metadata: namespace: <your-namespace>
- Prose: "the namespace where Headlamp is installed"

Out-of-scope references left untouched:
- kube-system in NetworkPolicy selectors (API server namespace)
- polaris namespace references (upstream workload namespace)
- Source code and test files

Refs: PRI-433

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

* docs: fix remaining hardcoded headlamp namespace to <your-namespace> placeholder

Prior commit was inconsistent — some files used <your-namespace> while
DEPLOYMENT.md, TROUBLESHOOTING.md and several troubleshooting/user-guide
docs still hardcoded headlamp as the namespace.

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

---------

Co-authored-by: Chris Farhood <chris@farhood.org>
Co-authored-by: Paperclip <noreply@paperclip.ing>

docs/getting-started/quick-start.md

@@ -38,7 +38,7 @@ EOF
 
 # Update Headlamp
 helm upgrade --install headlamp headlamp/headlamp \
-  --namespace kube-system \
+  --namespace <your-namespace> \
   --values headlamp-values.yaml
 ```
 
@@ -70,7 +70,7 @@ metadata:
 subjects:
   - kind: ServiceAccount
     name: headlamp
-    namespace: kube-system
+    namespace: <your-namespace>
 roleRef:
   kind: Role
   name: polaris-proxy-reader
@@ -111,7 +111,7 @@ EOF
 
 ```bash
 # Verify plugin files exist
-kubectl -n kube-system exec -it deployment/headlamp -c headlamp -- \
+kubectl -n <your-namespace> exec -it deployment/headlamp -c headlamp -- \
   ls /headlamp/plugins/headlamp-polaris-plugin/dist/
 
 # Expected output:
@@ -119,7 +119,7 @@ kubectl -n kube-system exec -it deployment/headlamp -c headlamp -- \
 
 # Verify RBAC is correct
 kubectl auth can-i get services/proxy \
-  --as=system:serviceaccount:kube-system:headlamp \
+  --as=system:serviceaccount:<your-namespace>:headlamp \
   -n polaris \
   --resource-name=polaris-dashboard
 
@@ -185,7 +185,7 @@ Cluster score badge in top navigation:
 
 ```bash
 # Verify plugin files exist
-kubectl -n kube-system exec -it deployment/headlamp -c headlamp -- \
+kubectl -n <your-namespace> exec -it deployment/headlamp -c headlamp -- \
   ls /headlamp/plugins/headlamp-polaris-plugin/
 
 # If missing, reinstall via Headlamp UI or sidecar method