Fix TypeScript error: Remove unused useState import from PDFViewer component

- Removed unused useState import that was causing build failures
- Fixed Docker deployment issue where pnpm build was failing with exit code 1
- All TypeScript checks now pass successfully

frontend/src/components/PDFViewer.tsx

@@ -1,6 +1,6 @@
 'use client';
 
-import React, { useState, useEffect } from 'react';
+import React, { useEffect } from 'react';
 import { X, Download, FileText } from 'lucide-react';
 
 interface PDFViewerProps {