[Feature]: Vercel deployment from main

[luchobonatti]

User story / Problem statement

Bounty judges need a live URL to interact with the dApp on Sepolia without running it locally. Vercel provides zero-config deployment for Next.js.

Proposed solution

1. Connect BootNodeDev/cops-monorepo to Vercel
2. Set root directory to packages/nextjs
3. Configure NEXT_PUBLIC_ env vars in Vercel dashboard
4. Auto-deploy triggers on every push to main

Required env vars in Vercel:

NEXT_PUBLIC_CHAIN_ID=11155111
NEXT_PUBLIC_CONFIDENTIAL_PAYROLL_ADDRESS=<from deployments/sepolia.json>
NEXT_PUBLIC_CONFIDENTIAL_USDC_ADDRESS=<from deployments/sepolia.json>
NEXT_PUBLIC_MOCK_USDC_ADDRESS=<from deployments/sepolia.json>

Acceptance criteria

• Vercel project connected to repo, auto-deploys on push to main
• Live URL loads and RainbowKit connects to Sepolia
• /employer and /employee routes accessible
• All NEXT_PUBLIC_ env vars set in Vercel dashboard
• Preview deployments work for PRs

Technical notes

• No server-side code — fully static next export compatible
• Reference: docs/PRD.md §6.1

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Part of Epic #15 — Infra