feat: make Cloudflare host configurable per office via env

Each office sets VITE_CLOUDFLARE_HOST and CLOUDFLARE_HOST in their
local .env files instead of hardcoding the subdomain in source code.

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

apps/Backend/.env.example

@@ -1,6 +1,7 @@
 NODE_ENV="development"
 HOST=0.0.0.0
 PORT=5000
+CLOUDFLARE_HOST=
 FRONTEND_URLS=http://localhost:3000
 SELENIUM_AGENT_BASE_URL=http://localhost:5002
 JWT_SECRET = 'dentalsecret'