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>

components/bible/reading-view.tsx

@@ -137,7 +137,7 @@ export function ReadingView({
             onMouseEnter={() => setHoveredVerseNum(verse.verseNum)}
             onMouseLeave={() => setHoveredVerseNum(null)}
             style={{
-              backgroundColor: (verse as any).highlight ? COLOR_MAP[(verse as any).highlight.color] : 'transparent',
+              backgroundColor: (verse as any).highlight ? COLOR_MAP[(verse as any).highlight.color as HighlightColor] : 'transparent',
               padding: '0.25rem 0.5rem',
               borderRadius: '4px',
               cursor: 'pointer',