ci: Publish prebuilt assets for Pilot

Build the app's assets in CI for each push and publish them on the release assets-<branch>, so Pilot benches download them instead of building on the server.

.github/workflows/assets.yml

@@ -0,0 +1,15 @@
+name: Pre-build assets
+
+on:
+  push:
+    branches: [develop, main]
+
+jobs:
+  assets:
+    name: Pre-build assets
+    uses: frappe/pilot/.github/workflows/app-assets.yml@develop
+    with:
+      # main supports Frappe v15 and v16; Pilot benches run v16 or later.
+      frappe-branch: ${{ github.ref_name == 'main' && 'version-16' || 'develop' }}
+    permissions:
+      contents: write