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/test-utils.tsx

@@ -1,4 +1,3 @@
-import React from 'react';
 import { AuditData, Result } from './api/polaris';
 
 // --- Fixtures ---
@@ -25,37 +24,3 @@ export function makeAuditData(results: Result[]): AuditData {
     Results: results,
   };
 }
-
-// --- Mock Polaris Context Provider ---
-
-interface MockPolarisProviderProps {
-  data?: AuditData | null;
-  loading?: boolean;
-  error?: string | null;
-  children: React.ReactNode;
-}
-
-// We dynamically import PolarisDataContext to inject mock values.
-// This avoids mocking the hook module — we supply real context with controlled values.
-const PolarisDataContext = React.createContext<{
-  data: AuditData | null;
-  loading: boolean;
-  error: string | null;
-} | null>(null);
-
-export function MockPolarisProvider({
-  data = null,
-  loading = false,
-  error = null,
-  children,
-}: MockPolarisProviderProps) {
-  return (
-    <PolarisDataContext.Provider value={{ data, loading, error }}>
-      {children}
-    </PolarisDataContext.Provider>
-  );
-}
-
-// The context reference used in test-utils must be the SAME object the components import.
-// We achieve this by having component tests mock `usePolarisDataContext` to read from our context.
-export { PolarisDataContext };