ci: add "build" workflows (#24)

.github/workflows/build-frontend.yml

@@ -0,0 +1,31 @@
+name: Build Frontend (Client)
+
+on:
+  pull_request:
+    branches:
+      - main
+
+jobs:
+  build-frontend:
+    runs-on: ubuntu-latest
+    defaults:
+      run:
+        working-directory: './client'
+    strategy:
+      matrix:
+        node-version: [20.x]
+    steps:
+      - name: Check out code
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+          clean: true
+
+      - name: Use Node.js ${{ matrix.node-version }}
+        uses: actions/setup-node@v4
+        with:
+          node-version: ${{ matrix.node-version }}
+          cache: 'npm'
+          cache-dependency-path: './client/package-lock.json'
+      - run: npm ci
+      - run: npm run build