fix: revert docs namespace to kube-system and use KUBE_VIP_NAMESPACE constant

Revert namespace references from headlamp back to kube-system in docs since
kube-vip workload runs in kube-system namespace (not headlamp which is the
Headlamp plugin install namespace).

Changes:
- CLAUDE.md: revert data sources and key constants namespace
- README.md: revert requirements line and troubleshooting table
- SECURITY.md: revert plugin scope namespaces
- OverviewPage.tsx: use KUBE_VIP_NAMESPACE constant instead of hardcoded string

Fixes PRI-562

SECURITY.md

@@ -12,10 +12,10 @@ This plugin is **read-only**. It does not perform any write operations against t
 
 - Services (type: LoadBalancer)
 - Nodes
-- Pods in `headlamp`
-- DaemonSets in `headlamp`
-- Leases in `headlamp`
-- ConfigMaps in `headlamp`
+- Pods in `kube-system`
+- DaemonSets in `kube-system`
+- Leases in `kube-system`
+- ConfigMaps in `kube-system`
 
 All data is fetched through Headlamp's built-in API proxy, which respects the user's existing RBAC permissions.