feature: review app

A suggestion that may provide a useful addition to your .gitlab-ci.yml: Implement a review app, that runs a job e.g. on each merge-request that compiles the demo and gives you a non-local version of the final .pdf.

I'm happy to send you a merge request implementing this feature. It's a good addition, for example if you set your main branch to protected and allow new additions only via MRs.