docs(onchainkit): add Deploy to Vercel checklist

[timkot]

What changed? Why?

• Adds a new doc page: docs/onchainkit/guides/deploy-to-vercel-checklist.mdx.
• Purpose: a concise, copy-pasteable checklist to ship OnchainKit/Next.js apps on Vercel without common pitfalls.
• Consolidates required env vars (NEXT_PUBLIC_BASE_RPC_URL, NEXT_PUBLIC_URL, NEXT_PUBLIC_ONCHAINKIT_PROJECT_NAME, and contract address vars), Node 20 requirement, wallet-connect sanity, and frequent gotchas (404s for frames/mini-apps, RPC limits, wrong chain id).

Notes to reviewers

• Location chosen under onchainkit/guides; happy to move if you prefer another section.
• Wording kept short/imperative (checklist style). I can expand with screenshots or link to the Onchain App Template if desired.
• Open to adding a short “Troubleshooting” table or a “One-click Vercel deploy” button if that fits docs patterns.

How has it been tested?

• Followed this checklist to deploy a minimal OnchainKit/Next.js app; verified env variables and wallet connect flow.
• Local docs preview renders correctly (MDX). No build/tooling changes outside this page.

Checklist

• Docs-only change
• No secrets or keys included
• Uses existing docs tone and heading levels

[cb-heimdall]

🟡 Heimdall Review Status

Requirement	Status	More Info
Reviews	🟡 0/2	Denominator calculation Show calculation 1 if user is bot 0 1 if user is external 0 2 if repo is sensitive 0 From .codeflow.yml 1 Additional review requirements Show calculation Max 0 0 From CODEOWNERS 0 Global minimum 0 Max 1 1 1 if commit is unverified 1 Sum 2

[ericbrown99]

either shorten the title or add a sidebarTitle: "Deploy to Vercel" line to the frontmatter

[ericbrown99]

Please remove emojis from headers

[ericbrown99]

Thanks for contributing! Please resolve the feedback. Also please ensure that your commits are signed and your key is configured in github for commits in the PR to be considered verified. This is required for us to merge