cli to login and save session

[matin]

to have a running MCP, we first name a simple way to login and save the tokens from a cli vs having to use ipython

1. command: garth login that's available through uvx garth. running garth without login should display a menu to choose the command, current only login
2. check if we can find saved tokens. if so, attempt to use them. if valid, confirm if those tokens should be used
3. if new login, start by confirming China or not China. then email, password and mfa
4. provide option to either save session with the ability to define the location or use the default ~/.garth or print the token