"flash" errors

[cryptix]

not in the sense of adobe flash but a way to add error/validation messages to a page (like name taken or login incorrect).

Right now we just render an error page with a back button.

[cryptix]

Not sure if it's even needed at this stage but feels like a massive quality of life improvement for users later.

[staltz]

Yes, I thought about this too, like if you input an incorrect SSB ID. Not a big priority, but a nice to have.