fix: comprehensive code quality, theming, and test coverage improvements

- Fix ExemptionManager apiVersion bug (apps/batch resources used wrong API path)
- Replace resource: any with proper KubeResource interface (strict TypeScript)
- Replace all var(--mui-palette-*) CSS variables with useTheme() + theme.palette.*
- Replace custom drawer with MUI Drawer component (proper a11y and theming)
- Replace alert() calls with StatusLabel-based inline feedback
- Add PolarisErrorBoundary wrapping all registered plugin components
- Export getPolarisApiPath/isFullUrl from polaris.ts, deduplicate in PolarisSettings
- Fix PolarisDataContext test mock missing triggerRefresh
- Fix DashboardView test SimpleTable mock using any
- Remove dead NamespaceDetailView (replaced by drawer), unused MockPolarisProvider,
  unused getSeverityColor export
- Add tests for InlineAuditSection, AppBarScoreBadge, topIssues, checkMapping (32 new)
- Update CLAUDE.md, CHANGELOG.md, README.md for v0.6.0

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

src/components/PolarisSettings.test.tsx

@@ -8,6 +8,18 @@ vi.mock('@kinvolk/headlamp-plugin/lib', () => ({
   ApiProxy: { request: vi.fn() },
 }));
 
+vi.mock('@mui/material/styles', () => ({
+  useTheme: () => ({
+    palette: {
+      primary: { main: '#1976d2', contrastText: '#fff' },
+      text: { primary: '#000', secondary: '#666' },
+      action: { disabledBackground: '#e0e0e0', disabled: '#9e9e9e' },
+      divider: '#e0e0e0',
+      background: { paper: '#fff' },
+    },
+  }),
+}));
+
 // Mock Headlamp CommonComponents
 vi.mock('@kinvolk/headlamp-plugin/lib/CommonComponents', () => ({
   SectionBox: ({ title, children }: { title?: string; children?: React.ReactNode }) => (