ci: upgrade actions to v4 and add CI badge

[AdekunleBamz]

Summary

Upgraded deprecated GitHub Actions and improved documentation visibility.

Changes

• node.js.yml: Upgraded actions/checkout and actions/setup-node from v3 to v4
• e2e-tests.yml: Upgraded actions/checkout and actions/setup-node from v3 to v4
• README.md: Added Node.js CI workflow status badge

Why

• v3 actions are deprecated and will stop working
• v4 includes performance improvements and Node.js 20 support
• CI badge provides instant visibility of build status

[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

[vercel]

@BamzzStudio is attempting to deploy a commit to the Coinbase Team on Vercel.

A member of the Team first needs to authorize it.