fix: resolve 6 E2E failures — cluster URL prefix + settings registration (#51)

Two root causes for the remaining 6 E2E failures after PR #50:

1. AppBarScoreBadge: Router.createRouteURL('polaris') was called without
   the cluster parameter, producing '/polaris' instead of '/c/main/polaris'.
   Now uses K8s.useCluster() to pass the active cluster. (appbar.spec.ts:18)

2. Plugin settings: registerPluginSettings was called with 'polaris' but
   the package.json name is 'headlamp-polaris'. Headlamp matches settings
   registrations to the package name, so the component never rendered.
   (settings.spec.ts — all 5 tests)

Co-authored-by: gandalf-the-greybeard[bot] <gandalf-the-greybeard[bot]@users.noreply.github.com>
Co-authored-by: Paperclip <noreply@paperclip.ing>

src/components/AppBarScoreBadge.test.tsx

@@ -7,8 +7,12 @@ import { makeAuditData, makeResult } from '../test-utils';
 // Mock Headlamp lib
 vi.mock('@kinvolk/headlamp-plugin/lib', () => ({
   ApiProxy: { request: vi.fn() },
+  K8s: {
+    useCluster: () => 'test-cluster',
+  },
   Router: {
-    createRouteURL: (name: string) => `/c/test-cluster/${name}`,
+    createRouteURL: (name: string, params?: { cluster?: string }) =>
+      `/c/${params?.cluster ?? 'default'}/${name}`,
   },
 }));