Add manual frontend build workflow

.github/workflows/frontend-build.yml

@@ -0,0 +1,43 @@
+name: Frontend Build
+
+on:
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+concurrency:
+  group: frontend-build-${{ github.ref }}
+  cancel-in-progress: true
+
+env:
+  ASTRO_TELEMETRY_DISABLED: '1'
+
+jobs:
+  build:
+    name: Build frontend
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Setup Bun
+        uses: oven-sh/setup-bun@v2
+        with:
+          bun-version: 1.3.11
+
+      - name: Install dependencies
+        run: bun install --frozen-lockfile
+
+      - name: Build frontend
+        run: bun run build
+
+      - name: Upload build output
+        uses: actions/upload-artifact@v4
+        with:
+          name: frontend-build-${{ github.run_id }}
+          path: |
+            dist
+            .vercel/output
+          if-no-files-found: error