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/troubleshooting/README.md

@@ -45,10 +45,10 @@ kubectl auth can-i get services/proxy \
 # Expected output: yes
 
 # 4. Check Headlamp pod is running
-kubectl -n headlamp get pods -l app.kubernetes.io/name=headlamp
+kubectl -n <your-namespace> get pods -l app.kubernetes.io/name=headlamp
 
 # 5. Check Headlamp logs for plugin errors
-kubectl -n headlamp logs deployment/headlamp | grep -i polaris
+kubectl -n <your-namespace> logs deployment/headlamp | grep -i polaris
 
 # Expected: No errors
 ```
@@ -57,7 +57,7 @@ kubectl -n headlamp logs deployment/headlamp | grep -i polaris
 
 ```bash
 # Verify plugin files exist
-kubectl -n headlamp exec deployment/headlamp -c headlamp -- \
+kubectl -n <your-namespace> exec deployment/headlamp -c headlamp -- \
   ls -la /headlamp/plugins/headlamp-polaris-plugin/
 
 # Expected output: