Stage 7: CI (GitHub Actions)

- Add .github/workflows/ci.yml: runs on PRs and pushes to main
- Installs deps (npm ci), runs lint (eslint) and build (next build,
  which also runs the TypeScript check)
- Node 26 to match the local dev environment, npm dependency caching

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Author: psatomas

.github/workflows/ci.yml

@@ -0,0 +1,28 @@
+name: CI
+
+on:
+  pull_request:
+  push:
+    branches: [main]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: "26"
+          cache: "npm"
+
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Lint
+        run: npm run lint
+
+      - name: Build
+        run: npm run build