Add missing setup-node steps to CI and Demo workflows

- Added actions/setup-node@v6 to Build job in CI workflow
- Added actions/setup-node@v6 to build job in Demo workflow
- Ensures correct Node version (22.18) is used in all jobs

Co-authored-by: fregante <1402241+fregante@users.noreply.github.com>

Author: Copilot

.github/workflows/ci.yml

@@ -29,6 +29,9 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v6
+      - uses: actions/setup-node@v6
+        with:
+          node-version-file: package.json
       - run: npm ci
       - run: npm run build
       - name: Ensure that test URLs aren't included in the built file

.github/workflows/demo.yml

@@ -16,6 +16,9 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v6
+      - uses: actions/setup-node@v6
+        with:
+          node-version-file: package.json
       - run: npm ci
       - run: npm run build:demo
       - run: npm run test:demo