External browsers were hitting localhost:5000 instead of going through
nginx. VITE_API_BASE_URL_BACKEND is now empty so all API calls use
relative /api/ paths that nginx proxies to the backend. Also adds
https://communitydentistsoflowell.mydentalofficemanagement.com to
FRONTEND_URLS for CORS. Updated .env.example to match so setup from
template doesn't silently revert this fix.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>