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/polaris.ts

@@ -300,7 +300,7 @@ export function computeScore(counts: ResultCounts): number {
  *
  * @returns Full path to results.json endpoint
  */
-function getPolarisApiPath(): string {
+export function getPolarisApiPath(): string {
   const baseUrl = getDashboardUrl();
   return baseUrl.endsWith('/') ? `${baseUrl}results.json` : `${baseUrl}/results.json`;
 }
@@ -311,7 +311,7 @@ function getPolarisApiPath(): string {
  * @param url - URL to check
  * @returns true if full URL, false if relative path
  */
-function isFullUrl(url: string): boolean {
+export function isFullUrl(url: string): boolean {
   return url.startsWith('http://') || url.startsWith('https://');
 }