Add GitHub Actions CI workflow

[AngusHsu]

Description

Create a GitHub Actions workflow at .github/workflows/ci.yml that runs on push and PR.

CI steps

1. Checkout code
2. Setup Node.js 22
3. npm ci
4. npm run lint
5. npm run test
6. npm run build

Triggers

• Push to main
• Pull requests targeting main

Depends on

• Configure ESLint and npm scripts #3 (npm scripts configured)
• Add unit tests for query_festival tool #8 (tests exist)

Acceptance Criteria

• .github/workflows/ci.yml exists
• CI runs lint, test, build in order
• CI passes on push to main