Epic: Vercel preview deployments for frontend PRs

[trillium]

Overview

Enable Vercel preview deployments so maintainers and contributors can see frontend changes deployed automatically on each PR. Preview deployments will proxy API requests to the existing dev backend, giving reviewers a live, functional app without needing a local setup.

Action Items (in dependency order)

1. Create Vercel account under Hack for LA org Gmail and link VRMS repo #2147 — Create a Vercel account under the Hack for LA org Gmail and link the repo
2. Add Vercel preview deployments for faster PR feedback #2145 — Add Vercel config, build fixes, and gitignore updates for preview deployments (blocked by Create Vercel account under Hack for LA org Gmail and link VRMS repo #2147)

Resources/Instructions

• Vercel Preview Deployments docs