fix(deploy): remove root vercel.json that broke world-model-gym builds

The root vercel.json (framework: null, buildCommand: "") was overriding
the Next.js framework detection for the world-model-gym project on
GitHub auto-deploys, causing 0ms builds and 404s on all pages.

Removed vercel.json and index.html (redirect stub) and deleted the
unnecessary research-project Vercel project that used them.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: biru-codeastromer