fix: badge navigation uses window.location.pathname for cluster extraction

* fix: badge navigation uses window.location + correct settings plugin name

- AppBarScoreBadge: Read cluster from window.location.pathname instead of
  useCluster() (returns null in AppBar context) or useLocation() (may not
  reflect cluster prefix outside cluster route context)
- registerPluginSettings: Use 'polaris' to match the deployed directory name
  (plugin is at static-plugins/polaris, not headlamp-polaris)
- Add unit test for no-cluster fallback navigation

Supersedes the source-code fixes from PR #55 without the workflow/deploy
script changes that broke CI.

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

* fix: use Object.defineProperty for window.location in test

Replace `as Location` cast with Object.defineProperty to match the
existing beforeEach pattern and fix TypeScript strict mode error.

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

---------

Co-authored-by: Gandalf the Greybeard <gandalf@privilegedescalation.dev>
Co-authored-by: Paperclip <noreply@paperclip.ing>

src/components/AppBarScoreBadge.tsx

@@ -1,10 +1,21 @@
-import { K8s, Router } from '@kinvolk/headlamp-plugin/lib';
 import { useTheme } from '@mui/material/styles';
 import React from 'react';
 import { useHistory } from 'react-router-dom';
 import { computeScore, countResults } from '../api/polaris';
 import { usePolarisDataContext } from '../api/PolarisDataContext';
 
+/**
+ * Extract the cluster name from the current browser URL.
+ * Headlamp cluster routes follow the pattern /c/<cluster>/...
+ * We read window.location.pathname directly because the AppBar renders
+ * outside the cluster route context, so useCluster() returns null and
+ * React Router's useLocation() may not reflect the cluster prefix.
+ */
+function getClusterFromUrl(): string | null {
+  const match = window.location.pathname.match(/\/c\/([^/]+)/);
+  return match ? match[1] : null;
+}
+
 /**
  * App bar badge showing cluster Polaris score
  * Clicking navigates to the overview dashboard
@@ -13,7 +24,6 @@ export default function AppBarScoreBadge() {
   const theme = useTheme();
   const { data, loading } = usePolarisDataContext();
   const history = useHistory();
-  const cluster = K8s.useCluster();
 
   if (loading || !data) {
     return null; // Graceful degradation when Polaris unavailable
@@ -36,7 +46,9 @@ export default function AppBarScoreBadge() {
   };
 
   const handleClick = () => {
-    history.push(Router.createRouteURL('polaris', { cluster: cluster ?? '' }));
+    const cluster = getClusterFromUrl();
+    const prefix = cluster ? `/c/${cluster}` : '';
+    history.push(`${prefix}/polaris`);
   };
 
   return (