vendor: move CDN deps to local, add download script

- Replace 5 unpkg.com CDN links with ./vendor/* local paths
- Add ./ prefix to all 9 local CSS/JS resources
- Add acpx-g/download.sh to fetch vendor deps
- Run download.sh in release-acpx-g workflow before build
- gitignore vendor/ (downloaded at build time, not committed)

Author: KonghaYao

acpx-g/download.sh

@@ -1,5 +1,6 @@
 #!/usr/bin/env bash
 set -euo pipefail
+mkdir -p "$(dirname "$0")/static/vendor"
 cd "$(dirname "$0")/static/vendor"
 
 # Download vendor JS/CSS from unpkg.com into current directory.