chore(ci): add Storybook build check workflow

[MuzzaiyyanHussain]

This PR adds a GitHub Actions workflow that runs pnpm build-storybook
to verify Storybook builds successfully on every PR and push.

✅ Helps catch broken stories early
✅ Keeps UI components in sync
✅ Follows existing CI conventions in .github/workflows

[vercel]

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

A member of the Team first needs to authorize it.

[cb-heimdall]

🟡 Heimdall Review Status

Requirement	Status	More Info
Reviews	🟡 0/1	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