Confusing UI after Google sign-up: Welcome screen overlaps with sign-up form

## Description
After signing up using the Google vendor login button, the Welcome to the Internet Archive screen appears on top of the Sign Up form.

Because the sign-up form is still visible in the background, it can confuse users and make them think they still need to complete the form again, even though they have already authenticated using Google.

## Steps to Reproduce
1. Go to the Open Library **Sign Up** page.
2. Click **Sign up with Google**.
3. Complete the Google authentication process.
4. After successful authentication, the **Welcome to the Internet Archive** screen appears.
5. The **Sign Up form** is still visible behind the welcome screen.

## Actual Behavior
- The welcome screen overlaps with the sign-up form.
- The sign-up form remains visible in the background.
- This may cause confusion for users who might try to fill out the form again.

## Expected Behavior
After signing up with Google:
- The user should be redirected to the home/dashboard page, **or**
- The welcome screen should appear without the sign-up form visible behind it.

## Relevant Designs

## Suggested Improvement
Hide or remove the sign-up form once vendor authentication (Google sign-up) is successful, or redirect the user to a dedicated welcome or dashboard page.

Implementation & Decision Details

#### Decisions

#### Stakeholders

@lokesh