I apologize if the answer to this question is obvious, but how do I work on a project in Particle Dev that was started in the online editor? Is there a better way to do this than copying and pasting my code into a new file?
Nope, there isn’t yet.
I think Particle is working on adding GitHub support to the Web IDE. This way you could work with the same code in the Web IDE and Particle Dev.
Alternatively, you could use Cloud 9 https://c9.io
It gives you an Ubuntu workspace, a text editor, and a terminal. You could use it to work on a repository, and install particle-cli in it do build code and flash to devices.