feat: consolidate dashboard pages, fix namespace links, add tests

Merge Overview and Full Audit into a single dashboard page that always
shows the skipped check count. Fix namespace link 404s by using
Headlamp's Link component (which generates cluster-prefixed URLs)
instead of raw react-router-dom Link. Add vitest unit tests for all
polaris.ts utility functions.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/components/NamespaceDetailView.tsx

@@ -118,6 +118,10 @@ export default function NamespaceDetailView() {
               name: 'Danger',
               value: <StatusLabel status="error">{counts.danger}</StatusLabel>,
             },
+            {
+              name: 'Skipped',
+              value: <StatusLabel status="">{counts.skipped}</StatusLabel>,
+            },
           ]}
         />
       </SectionBox>