Add CI pipeline with test, lint, and build checks on every PR

[Just-Bamford]

Summary

The core repo has 28 passing tests across backend and frontend, an
ESLint config, and a TypeScript build — but no CI pipeline. There is
no GitHub Actions workflow file anywhere in the repo. This means every
PR merged to main could silently break tests, introduce lint errors, or
fail the TypeScript build without any automated check catching it before
merge. For a project handling cryptographic voter data, a broken test
suite merging silently is a serious quality gap.

Scope

• Add a .github/workflows/ci.yml workflow that runs on every PR
  targeting main
• Specify Node.js 20.x in the workflow using
  uses: actions/setup-node@v4 with node-version: '20' — this
  matches the required version in the README
• The workflow should run in sequence: install dependencies, lint,
  build, test
• Backend steps: cd backend && npm install, npm run lint,
  npm run build, npm run test:backend — requires a PostgreSQL
  service container in the workflow
• Frontend steps: cd frontend && npm install, npm run lint,
  npm run build, npm run test:frontend
• Add a PostgreSQL service in the workflow using
  services: postgres:15 with the same credentials as .env.example
  so backend tests can run against a real database
• Run Prisma migrations before backend tests:
  npx prisma migrate deploy
• Add a CI badge to the README pointing to the workflow status

Relevant Files

• .github/workflows/ci.yml (new file)
• README.md
• backend/package.json
• frontend/package.json

Acceptance Criteria

• CI workflow runs on every PR to main
• Backend lint, build, and tests all run and pass
• Frontend lint, build, and tests all run and pass
• PostgreSQL service container is correctly configured
• Prisma migrations run before backend tests
• CI badge added to README and resolves green
• A PR with a failing test is blocked from merging by the workflow

Out of Scope

• Deployment automation — CI only, no CD
• Coverage reporting — a separate issue

Note for Contributors

The PostgreSQL service container must use the exact same DATABASE_URL
format as .env.example. Do not hardcode credentials differently from
what the test suite expects — the tests should pass locally and in CI
with the same configuration.

[Dickson2015]

I would love to work on this issue.

[grantfox-oss]

🦊 GrantFox — @Dickson2015 has been assigned to this issue as part of the Official Campaign | FWC26 campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #31)
2. Your PR will be reviewed by the AnonVote maintainers

Good luck! Track your progress on GrantFox.