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

CLAUDE.md

@@ -8,7 +8,7 @@ Headlamp plugin for kube-vip virtual IP and load balancer visibility. Read-only
 
 - **Plugin name**: `kube-vip`
 - **Target**: Headlamp >= v0.26
-- **Data sources**: kube-vip DaemonSet/pods in `headlamp`, Services (type:LoadBalancer), Nodes, Leases, `kubevip` ConfigMap
+- **Data sources**: kube-vip DaemonSet/pods in `kube-system`, Services (type:LoadBalancer), Nodes, Leases, `kubevip` ConfigMap
 - **Reference plugin**: `../headlamp-polaris-plugin`
 
 ## Commands
@@ -58,7 +58,7 @@ kube-vip uses **no CRDs**. All state comes from standard Kubernetes resources an
 
 ## Key constants (src/api/k8s.ts)
 
-- Namespace: `headlamp`
+- Namespace: `kube-system`
 - DaemonSet name: `kube-vip-ds`
 - Cloud provider name: `kube-vip-cloud-provider`
 - ConfigMap name: `kubevip`