fix: use pdf-parse v2 API (PDFParse class, not default export)

🔧 v4.3: Web app deep audit — 12 bugs fixed (4 critical) (#6)

feat: add user authentication checks and improve navigation with logout functionality

Build all missing features: PDF/DOCX upload, team system (5 seats, invites, shared dashboard), API keys (generate/revoke/limits), custom clause rules (CRUD + regex)