Sure there are foss qr code generators, I don’t know any at the moment but with a simple google search you should find what you want. About the pdf on a specific page, I think you can add #page={pageNumber} in the url and should open it at the given page.
Sounds nice! I am also working on a usenet indexer right now, but I am not ready to make it public. Anyway, if you publish a docker container I would gladly give it a try.