Add signup profile fields

[neethika12]

What changed

Adds lightweight profile fields to the signup experience so new users can provide clearer identity details during account creation.

Why it changed

Sentinent benefits from having basic profile context available early for workspace collaboration and signal attribution, and the signup form now reflects that need without becoming overly heavy.

User impact

• Users can now enter a required full name during signup.
• Users can optionally provide a job title and organization or team.
• The optional fields are stacked on separate lines for a cleaner, clearer layout.

Technical notes

• Extends signup form state and validation in the auth component.
• Sends the new profile fields with the existing signup request.
• Updates frontend tests for the new required full-name field.

Validation

• npm test -- --watch=false