Add basic build workflow

.github/workflows/ci.yml

@@ -0,0 +1,46 @@
+name: React Planner CI
+
+on:
+  push:
+
+jobs:
+  build:
+    name: Install dependencies and build
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Set up Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: "16.20.2"
+
+      - name: Install Yarn
+        run: npm install --global [email protected]
+
+      - name: Install dependencies
+        run: yarn install --frozen-lockfile --non-interactive
+
+      - name: Build project
+        run: yarn build
+
+      - name: Smoke test built application
+        run: |
+          python3 -m http.server 8080 --directory demo/dist > /tmp/server.log 2>&1 &
+          server_pid=$!
+          trap 'kill "$server_pid"' EXIT
+
+          for attempt in 1 2 3 4 5; do
+            if curl --fail --silent --show-error http://127.0.0.1:8080/ > /dev/null; then
+              echo "Smoke test passed"
+              exit 0
+            fi
+
+            sleep 1
+          done
+
+          echo "Smoke test failed"
+          cat /tmp/server.log
+          exit 1