Adapted demo build, export and static navigation code

Original project: OpenSCAD Customizer for Manyfold
Original author and copyright notice: Copyright (C) 2026 Max Dymond.
Original license: AGPL-3.0-only.
Original source revision: 41a967e1d76fd10924cce1f2605e0422c81bcf5e
https://github.com/cmeister2/manyfold_openscad/tree/41a967e1d76fd10924cce1f2605e0422c81bcf5e

Original files:
https://github.com/cmeister2/manyfold_openscad/blob/41a967e1d76fd10924cce1f2605e0422c81bcf5e/bin/build-demo
https://github.com/cmeister2/manyfold_openscad/blob/41a967e1d76fd10924cce1f2605e0422c81bcf5e/demo/run-host
https://github.com/cmeister2/manyfold_openscad/blob/41a967e1d76fd10924cce1f2605e0422c81bcf5e/demo/export.rb
https://github.com/cmeister2/manyfold_openscad/blob/41a967e1d76fd10924cce1f2605e0422c81bcf5e/demo/bootstrap.mjs

https://github.com/cmeister2/manyfold_openscad/blob/41a967e1d76fd10924cce1f2605e0422c81bcf5e/test/demo/serve.mjs

https://github.com/cmeister2/manyfold_openscad/blob/41a967e1d76fd10924cce1f2605e0422c81bcf5e/playwright.demo.config.mjs

https://github.com/cmeister2/manyfold_openscad/blob/41a967e1d76fd10924cce1f2605e0422c81bcf5e/.github/workflows/pages.yml

The corresponding files in manyfold_thumbnails adapt that demo pipeline to
export Manyfold's thumbnail gallery and format settings. The OpenSCAD renderer,
WebAssembly and Customizer code are not included. The original copyright and
AGPL-3.0-only license apply to the adapted demo code. This notice does not
declare a license for unrelated plugin code or for the thumbnail images, whose
separate source and license notices are retained alongside them.

Adapted source:
https://github.com/cmeister2/manyfold_thumbnails

The unchanged original license text is retained in
OPENSCAD-DEMO-AGPL-3.0.txt.