P5-01: Add .github/workflows/ci.yml
- Trigger on push and pull_request to main
- Runs on ubuntu-latest
P5-02: Add build-and-test job
- actions/checkout@v4, actions/setup-node@v4 (Node 20), npm cache
- npm ci, npm run build, npm test
Also: restrict vitest to src/ and exclude dist/ so CI passes (no .d.ts suites)
Co-authored-by: Cursor <cursoragent@cursor.com>