Added accessibility fix for form validation

What does this MR do and why?

Adds client-side validation to the group and project name fields on the "Import" tab and the "Create" tab to improve user experience and accessibility needs.

Changes:

• Validates group name and project name before form submission
• Displays inline error messages for empty required fields
• Prevents form reload when validation fails
• Improves accessibility with ARIA attributes
• Added additional underline styling to the focus box to match design system patterns.

References

Issue reference: 511716

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Ensure GDK is running in SaaS mode (https://docs.gitlab.com/ee/development/ee_features.html#simulate-a-saas-instance)
2. Sign in as admin and ensure that signs ups are enabled, admins are not required to confirm new users and import settings are allowed:
   1. select Admin
      • Select Settings > General
      • Expand the Import and export settings section
   2. Enable specific import sources - In the Import and export settings section, you need to:
      • Select each of the Import sources you want to allow (this determines which import options will be visible)
      • Select Save changes
3. Reload your GDK
4. At the login screen sign up for a new user account ( click "register")
5. Enter in the new user information
6. Complete screen at http://localhost:3000/users/sign_up/welcome and select "create a new project"
7. The next screen should bring up the "Create or import your first project"
8. Select the Import Tab
9. Delete the group name if there is one and then click off and the validation should appear.

MR acceptance checklist

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