docs: document vercel.app production support

[Railly]

Summary

Documents *.vercel.app production domain support for Clerk apps.

This updates the deployment docs so they no longer say Vercel-provided *.vercel.app domains cannot be used for production, and clarifies the supported behavior, limitations, and Next.js proxy matcher requirement.

Related PRs / landing order

These PRs are part of the *.vercel.app production support launch batch:

1. clerk_go AIE-934 - clerk/clerk_go#18546 - remove the per-instance email flag and keep the global kill switch as the only rollout control.
2. clerk_go AIE-932 - clerk/clerk_go#18547 - allow DAPI production instance creation with *.vercel.app provider domains.
3. dashboard AIE-932 - clerk/dashboard#9184 - allow the Dashboard production instance modal to submit my-app.vercel.app.
4. clerk-docs AIE-933 - this PR - document support, limitations, and the Next.js /__clerk matcher requirement.

Recommended order: land AIE-934 first, then the clerk_go DAPI support, then Dashboard, then publish these docs when the behavior is ready to announce.

Changes

• Update Vercel deployment docs to document *.vercel.app production support.
• Update production deployment docs to distinguish custom-domain production from Vercel provider-domain production.
• Document supported behavior: production mode, no manual DNS, sign-in/sign-up, and core auth emails through accounts.dev.
• Document limitations that still require a custom domain: custom email templates, email link auth, app invitations, organization invitations, and email template customization.
• Add the Next.js matcher requirement so auto-proxy traffic through /__clerk is not excluded.
• Add troubleshooting notes for live keys, domain sync, old SDKs, and missing matcher configuration.

Test plan

• pnpm prettier --check docs/guides/development/deployment/vercel.mdx docs/guides/development/deployment/production.mdx docs/guides/development/integrations/platforms/vercel-marketplace.mdx

Known local limitation: full docs build is blocked in my local checkout by an unrelated untracked file, docs/guides/ai/clerk-cli.mdx, which is not in the docs manifest.

Linear: AIE-933

[vercel]

The latest updates on your projects. Learn more about Vercel for GitHub.

Project	Deployment	Actions	Updated (UTC)
clerk-docs	Ready	Preview	May 6, 2026 8:46pm