Add CI workflow for backend tests and website lint/build

.github/workflows/ci.yml

@@ -0,0 +1,65 @@
+name: CI
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+concurrency:
+  # One CI run per branch/PR; superseded runs are cancelled to save minutes.
+  group: ci-${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  backend:
+    name: Backend tests
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: 22
+          cache: npm
+          cache-dependency-path: package-lock.json
+
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Run tests
+        run: npm test
+
+  website:
+    name: Website lint and build
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: 22
+          cache: npm
+          cache-dependency-path: website/package-lock.json
+
+      - name: Install dependencies
+        working-directory: website
+        run: npm ci
+
+      - name: Lint
+        working-directory: website
+        run: npm run lint
+
+      - name: Build
+        working-directory: website
+        env:
+          GITHUB_PAGES: true
+        run: npm run build

README.md

@@ -35,6 +35,7 @@ website/
   src/backendSamples.js  # GraphQL server samples in 10 backend languages
   vite.config.js   # Vite config (GitHub Pages base path + /graphql dev proxy)
 .github/workflows/
+  ci.yml           # Backend tests plus website lint/build on push and PRs
   deploy-pages.yml # Builds website/ and publishes it to GitHub Pages
 ```
 
@@ -105,6 +106,18 @@ npm run lint                      # Oxlint
 npm test
 ```
 
+## Continuous integration
+
+The [`CI`](.github/workflows/ci.yml) workflow runs on every push to `main`, on
+every pull request, and on demand from the Actions tab. It has two jobs:
+
+- **Backend tests** — `npm ci` then `npm test` (node:test) at the repository root.
+- **Website lint and build** — `npm ci`, `npm run lint` (Oxlint) and
+  `GITHUB_PAGES=true npm run build` inside `website/`, matching what the Pages
+  deployment builds.
+
+Runs are grouped per branch and superseded runs are cancelled automatically.
+
 ## Finance Cluster Integration (Priority 1)
 
 This service now exposes a unified finance GraphQL surface over three upstream