Docs: update all documentation and add overview
- README: add Frontend section, deploy script, docs links, status
- docs/README.md: new documentation overview (entry points, frontend, deployment)
- docs/EXPLORER_API_ACCESS.md: reference deploy-frontend-to-vmid5000.sh for frontend-only deploy
- docs/INDEX.md: add Frontend & Explorer section, fix Quick Start, Last Updated
- README_DEPLOYMENT: add docs/README, EXPLORER_API_ACCESS, deploy script, deployment guide
- frontend/FRONTEND_REVIEW.md: add post-review update (C1–L4 implemented)
Co-authored-by: Cursor <cursoragent@cursor.com>