chore: import upstream snapshot with attribution

.github/workflows/ui-build.yml

@@ -0,0 +1,48 @@
+name: UI Build
+
+on:
+  workflow_call:
+    inputs:
+      hf_ui_version:
+        description: 'Version string for version.json (e.g. 12345)'
+        required: false
+        type: string
+
+jobs:
+  build:
+    runs-on: ubuntu-slim
+    env:
+      BRANCH_NAME: ${{ github.head_ref || github.ref_name }}
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v6
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v6
+        with:
+          node-version: "24"
+          cache: "npm"
+          cache-dependency-path: "tools/ui/package-lock.json"
+
+      - name: Install dependencies
+        run: npm ci
+        working-directory: tools/ui
+
+      - name: Build application
+        env:
+          HF_UI_VERSION: ${{ inputs.hf_ui_version || '' }}
+          LLAMA_BUILD_NUMBER: ${{ inputs.hf_ui_version || 'b0000' }}
+        run: npm run build
+        working-directory: tools/ui
+
+      - name: Run PWA unit tests (versioned build output)
+        run: npx vitest --project=unit --run tests/unit/pwa.spec.ts
+        working-directory: tools/ui
+
+      - name: Upload built UI
+        uses: actions/upload-artifact@v6
+        with:
+          name: ui-build
+          path: tools/ui/dist/
+          retention-days: 1