Add Terms of Service and Privacy Policy

- Create TermsModal component with tabbed interface
- Add Terms of Service covering usage, data, liability
- Add Privacy Policy covering data collection and rights
- Update SignIn with clickable legal links and trust badges
- Fix: Add package-lock.json for CI builds

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: Raushan kumar