You seem to be coming at this from a notebook-centric view? I’m not following why? You don’t say what parts of JupyterLab you need to keep? Any? Because what you describe just seems to be traditional Python and javascript Django / Flask/etc. apps have been around a long time. You only need Python, javascript, css, HTML. Example Django-based app here where the text processing is done via Python code behind-the-scenes. Pythonanywhere.com has nice tutorials of making Python-backed apps.
For embedding widgets, see here and discussions here.
There’s also examples of linking out to code from pages? Have you seen JupyterBook or other related tech noted here.
If you want to make a webapp that is a notebook page, there are several options. The most integrated with Jupyter is Voila.There is a gallery here. Search ‘webapp’ in this discussion group for some more leads, such as here.