OWASP/threat-dragon ? reverse-engineered prompt

Build me the Threat Dragon app from this repo, a simple open source tool for threat modeling.

I want a web app where I can draw a data flow diagram, add elements to it, and attach threats, mitigations, and countermeasures to each part. It should feel easy to use and clean, like something a team could open in the browser and start modeling with right away. If it makes sense, keep the local file support working, and make the app ready to connect to GitHub, Bitbucket, GitLab, or GitHub Enterprise when those settings are provided.

Please make sure it runs locally from the top level of the project, with the frontend and backend both working, and that the main page loads on localhost as expected. If you need current setup details or docs, look them up online and follow the project guidance. Also keep the code organized and include sensible tests where it matters.