feat: restructure sidebar hierarchy and add full audit view

Reorganize the sidebar into a proper hierarchy (Overview, Full Audit,
Namespaces) and add a Full Audit dashboard view that includes skipped
checks. Namespace routes move to /polaris/ns/:namespace to avoid
path collisions, and namespace detail pages now link out to the
Polaris dashboard.

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

src/components/NamespaceDetailView.tsx

@@ -12,6 +12,7 @@ import {
   computeScore,
   countResultsForItems,
   filterResultsByNamespace,
+  POLARIS_DASHBOARD_PROXY,
   Result,
   ResultCounts,
 } from '../api/polaris';
@@ -82,6 +83,21 @@ export default function NamespaceDetailView() {
     <>
       <SectionHeader title={`Polaris — ${namespace}`} />
 
+      <SectionBox title="External">
+        <NameValueTable
+          rows={[
+            {
+              name: 'Polaris Dashboard',
+              value: (
+                <a href={POLARIS_DASHBOARD_PROXY} target="_blank" rel="noopener noreferrer">
+                  View in Polaris Dashboard
+                </a>
+              ),
+            },
+          ]}
+        />
+      </SectionBox>
+
       <SectionBox title="Namespace Score">
         <NameValueTable
           rows={[