add signup command

[kcmannem]

This is a tiny new command to help discover the sign up page. Chloe and I have decided that signup is not worth exploring at the moment as the industry has not settled on a strategy that is safe and secure yet.

Auth0 has not caught up with this requirement yet and none of the popular cli's I've explored have not supported this. Sign up security is based on browsers so its hard to translate it to a cli experience.

The new cloud auth signup command simply opens our sign up page.

[sdairs]

Hmmm...I'm not sure about this. I tested it and had claude code run the command, and its...a pretty weird experience. Almost feels like I had malware popping browsers open.

I think if we want to do this we need to either:

1. Create a sign up page variant that makes it more clear why this page is suddenly open - like clickhouse.cloud/signUp?from=cli or something - and shows more information about what you're looking at and why.... Otherwise the user has no context why they're there. Its just a random log in box.
2. Just print text with instructions for how to sign up with a clickable link.

I like 1 and I think it would be a better middle ground if we can do it.

[kcmannem]

This is the simplest solution I could come up with. What type of content would we have on a cli originated signup?
The intent is quite clear that its to sign up so I don't know if prompting the sign up page is uncalled for or out of the blue.

I'll delegate to Chloe or Design on if this version of the command is valuable.