Super impressive to follow the progress and to learn some of the thoughts that has to go into the architecture of the solution. It's definitely a huge task to take on building a new desktop wallet, but with all the source code of the existing on ready at hand, it should be possible to extract the parts you need and add your own.
For the contract building (and actually the potential integration to external systems' APIs too) I would suggest a bot. It makes it easy for users to simply add one bot from their wallet to then have access to everything that bot offers - including connections to external APIs.
With webhooks from GitHub, it would be quite straightforward to create an Oracle that propagates various events from GitHub to the Byteball DAG too.

I really think your project is incredibly interesting and I agree there's definitely an actual demand for smooth solutions for the problem you identified.

Good luck on the further progress and keep sharing as things progresses :)