Opt in the macOS App Sandbox

[NN708]

I would like to request enabling the App Sandbox for Syncthing. This feature provides additional security and aligns with macOS best practices.

[xor-gate]

This is a very good idea, but care must be taken when going this route so Syncthing for macOS can reach the folders and files as it needs extra use configuration the app is allowed to access outside the sandbox. It must be investigated and tested troughly.