CI: add a workflow that runs lint + build + tests on every PR

[AndresL230]

Problem

The only GitHub Actions workflow in this repo is .github/workflows/npm-publish.yml, which triggers on tag pushes (v*) for releasing to npm. There is no PR-validation workflow — npm run lint, npm run build, and npm run test are never run by CI.

Consequences:

• PRs can merge with broken tests as long as the author doesn't run them locally. We rely entirely on author discipline.
• A regression on main is only caught when someone next runs the suite locally or when a release goes out broken.
• Multi-Node-version compatibility (Node 18 / 20 / 22) is never verified. The interceptor code in particular hits undici / fetch edge cases that vary by Node version — see PR fix(interceptor): surgical fixes for Request body bytes + http.request overload edges (#10, #12) #35 (fetch(new Request(url, { body })) reports requestBytes: 0 #12) where the originally planned fix relied on undici behavior that was empirically different in Node 26 vs older docs.

Proposed workflow

.github/workflows/ci.yml:

name: CI
on:
 pull_request:
 push:
 branches: [main]
jobs:
 test:
 runs-on: ubuntu-latest
 strategy:
 matrix:
 node-version: [18, 20, 22]
 steps:
 - uses: actions/checkout@v4
 - uses: actions/setup-node@v4
 with: { node-version: ${{ matrix.node-version }} }
 - run: npm ci
 - run: npm run lint
 - run: npm run build
 - run: npm run test

Why three Node versions

• 18 — minimum supported per package.json engines
• 20 — current LTS
• 22 — current active

This catches Node-version-specific fetch/http behavior (the kind of thing PR #35 #12 ran into) before merge.

Acceptance

• ci.yml workflow file added
• Workflow runs on pull_request and push to main
• Tests pass on Node 18, 20, 22
• PR-required check status configured in repo settings (optional, but recommended)

Notes

This is one-file, additive, no code changes. Could fit under Wave 6 (polish / one-offs) in the roadmap alongside #14 and #2 — or land standalone whenever convenient.