Set up PR CI/CD and preview deployments

[leoncheng57]

Summary

Set up pull-request CI/CD for this Vite site so each PR gets automated validation and a preview deployment URL.

Problem

Right now the repo does not have repository-local CI workflows or per-PR preview deployments. PRs can show diffs, but there is no automatic lint/build verification owned by the repo and no ephemeral preview environment for reviewers.

Proposed approach

• add a GitHub Actions workflow to run npm ci, npm run lint, and npm run build on pull requests
• fix the current ESLint parsing baseline so CI can go green on TSX files
• configure Netlify to build the repo and publish docs for free PR preview deployments
• document the setup in the repo README

Implementation plan

Secret gist: https://gist.github.com/leoncheng57/087b861b12147811c4a2995266d512ec

Acceptance criteria

• every pull request triggers a GitHub Actions CI run
• CI validates lint and build successfully
• every pull request gets a Netlify preview URL
• the setup is documented for future maintenance