I could never get Java AIs working on Windows. Your best bet would still probably be either Lua (with Shard) or C++, I've built spring before (on MSVC x64 + VCPKG, which required some significant changes the cmakelists, and to streflop but that's another story...) and contributed to the engine (only a tiny bit though, like 2 years ago) so I know a little bit about the build process, but not much about the AI interfaces.
Shard isn't broken. It's not an AI. It's an AI _framework_. See 'AI/Skirmish/Shard/README.md' in the source files for details. From what I can see using Shard (you already know how to get it working, from what I can tell) would be the easiest way if you're willing to use Lua.
For C++, in theory, you could do something like this:
* Clone the maintainance branch of Spring off Github
* Make sure it builds
* Work from the 'AI/Skirmish/{YOUR AI NAME HERE}' folder
* Make your own AI using CppTestAI as a template
This way you'll have access to debug builds of both Spring and your AI. Hopefully you'll be able to do stuff like set breakpoints, etc. and develop much faster. As for developing with this process and Zero-K... that part I'm afraid you'll need to figure out yourself. A lot of people have trouble getting the Java AIs working apparently, but if you can get it working it could probably be simpler if you like Java.
sorry if I'm talking a bit out of my depth and misguided you, just want to help. good luck :)