fix(workflow): build frontend before building backend in demo deployment

.github/workflows/deploy-demo-server.yml

@@ -14,8 +14,38 @@ jobs:
       - name: Set up Go
         uses: actions/setup-go@v5
         with:
-          go-version: '1.22'
-      
+          go-version: '1.24'
+          cache: true
+
+      - name: Set up Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: '20'
+          cache: 'npm'
+          cache-dependency-path: 'frontend-modern/package-lock.json'
+
+      - name: Install frontend dependencies
+        run: npm --prefix frontend-modern ci
+
+      - name: Restore frontend build cache
+        uses: actions/cache@v4
+        with:
+          path: frontend-modern/dist
+          key: frontend-build-${{ hashFiles('frontend-modern/package-lock.json', 'frontend-modern/src/**/*', 'frontend-modern/index.html', 'frontend-modern/postcss.config.cjs', 'frontend-modern/tailwind.config.cjs') }}
+
+      - name: Build frontend
+        run: |
+          if [ -d "frontend-modern/dist" ] && [ -f "frontend-modern/dist/index.html" ]; then
+            echo "Using cached frontend build";
+          else
+            npm --prefix frontend-modern run build;
+          fi
+          
+          # Prepare embedding directory
+          rm -rf internal/api/frontend-modern
+          mkdir -p internal/api/frontend-modern
+          cp -r frontend-modern/dist internal/api/frontend-modern/
+
       - name: Build static binary
         run: CGO_ENABLED=0 go build -ldflags="-s -w" -o pulse cmd/pulse/main.go