Deploy readiness check

I'm deploying this app to [Vercel / Netlify / Cloudflare Pages / Replit / Render]. Before I do:

1. Run a production build locally and report any errors or warnings.
2. List every environment variable the app reads, whether it's public or secret, and which environment needs it.
3. Find hard-coded localhost / 127.0.0.1 / http:// URLs.
4. Check auth redirect/callback URLs and webhook URLs that must be updated for the production domain.
5. Check the Node version requirement and how to pin it on this host.
6. For a single-page app, confirm the host's fallback-to-index.html config exists.
Give me a numbered checklist of what I must do in the host dashboard.