Add it to Claude Design
Claude builds the design system for you from its files.
Add the "Things 3 (iOS)" design system to my Claude design systems. Its files, already in Claude's Design System format, are in https://github.com/feimacode/open-design-agent-kit/tree/main/claude-design-systems/things-3-ios/project. Build a Design System artifact from them.
Or in Claude's Add design system, pick the GitHub repo option with feimacode/open-design-agent-kit and the folder claude-design-systems/things-3-ios.