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/api/PolarisDataContext.test.tsx

@@ -16,6 +16,7 @@ vi.mock('./polaris', async importOriginal => {
       data: makeAuditData([makeResult()]),
       loading: false,
       error: null,
+      triggerRefresh: vi.fn(),
     })),
   };
 });
@@ -44,5 +45,6 @@ describe('usePolarisDataContext', () => {
     expect(result.current.data).not.toBeNull();
     expect(result.current.loading).toBe(false);
     expect(result.current.error).toBeNull();
+    expect(result.current.refresh).toBeDefined();
   });
 });