build: complete Phase 2.1 implementation and verify build

- Verified all exports in highlight-manager.ts are correct
- Installed @clerk/nextjs dependency for API routes
- Fixed TypeScript errors in API routes (NextRequest type)
- Fixed MUI Grid component usage in highlights-tab.tsx (replaced with Box flexbox)
- Fixed HighlightColor type assertion in reading-view.tsx
- Build completed successfully with no TypeScript errors

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

jest.config.js

@@ -0,0 +1,22 @@
+const nextJest = require('next/jest')
+
+const createJestConfig = nextJest({
+  // Provide the path to your Next.js app to load next.config.js and .env files in your test environment
+  dir: './',
+})
+
+// Add any custom config to be passed to Jest
+const customJestConfig = {
+  setupFilesAfterEnv: ['<rootDir>/jest.setup.js'],
+  testEnvironment: 'jest-environment-jsdom',
+  moduleNameMapper: {
+    '^@/(.*)$': '<rootDir>/$1',
+  },
+  testMatch: [
+    '**/__tests__/**/*.test.ts',
+    '**/__tests__/**/*.test.tsx',
+  ],
+}
+
+// createJestConfig is exported this way to ensure that next/jest can load the Next.js config which is async
+module.exports = createJestConfig(customJestConfig)