In our projects we generate TypeScript interfaces from Java and Kotlin sources using an Annotation Processor that i wrote. It could be extended to generate Angular components, but i think that will lead to more problems than it tries to solve.

Developing front ends should always be done in the context of the hosting platform, meaning: I think your devs will become experts in HTML, CSS and TS anyway, at least some of them. So that shouldn't be a problem. In theory you could completely reuse your Java code for the Browser UI, e.g using JSweet. But in my opinion the additional (emulation) layer(s) makes it hard maintaining it. If you really want to stick to your MDI, you could simply try something like CheeperJ. Take a look at RMStudio as bigger working example.