ci: run eslint on the playground JavaScript

Adds a lint-js job that installs the eslint devDependency and runs
"npm run lint" on static/js.

Author: sylvestre

.github/workflows/website.yml

@@ -228,6 +228,24 @@ jobs:
         name: wasm-${{ matrix.name }}
         path: wasm-out
 
+  lint-js:
+    name: Lint playground JavaScript
+    runs-on: ubuntu-latest
+    steps:
+    - name: Checkout uutils.github.io Repository
+      uses: actions/checkout@v7
+
+    - name: Set up Node.js
+      uses: actions/setup-node@v4
+      with:
+        node-version: 20
+
+    - name: Install dependencies
+      run: npm install
+
+    - name: Run ESLint
+      run: npm run lint
+
   build:
     name: Build website artifacts
     runs-on: ubuntu-latest