Improve signup screen error messages

[sudjoao]

Refactoring Proposal

Describe the design issue(s) you have identified in the code
When I tried to create an account, I receive a error message saying that the password was similiar to the user (image 1), but I didn't realize that I have received this error because the message is in the same color of the rest of the text, so iit s hard to find it.

Which source files are affected to this issue(s)?

1. src/ARte/users/jinja2/users/signup.jinja2

Describe refactoring alternatives to redesign the code

1. Make the error message more flashy, maybe changing the text color or using an alert.