Add custom "terminal/shell profile" option and font resize option for app ui

[fazle-rabbi-dev]

I'm a Nushell user, and there's currently no way to set a Nushell/custom shell profile and set as the default shell.

So, every time I open a new terminal, I have to run the nu command to switch to Nushell, which gets boring.

Please bring an option to add and set a custom shell profile.

The Paseo app already has an option to add custom shell profiles. It would be great to have the same feature in Emdash.