sreegjl/timelines ? reverse-engineered prompt

Build me a desktop app for making interactive timelines for worldbuilding and history.

I want users to be able to add events, spans, and eras, organize them with tags and groups, and attach notes or sources directly to each item. The notes should support Markdown, and it would be great if people could keep the files locally in plain JSON and Markdown so nothing depends on an account or cloud sync.

Please include a timeline canvas, a map view where events can have coordinates, and a spreadsheet style view for quickly editing dates and names. Let the app support themes too, so a timeline can have its own look. If it makes sense, add a browser viewer for opening a timeline file and sharing it. Use the current docs online if you need to, and make it feel polished enough for real use.