fix(AI Transparency Center): fix AI Transparency Center bugs

Follow up work from https://gitlab.com/gitlab-com/marketing/digital-experience/buyer-experience/-/issues/3499

Step 1: What is changing in this MR?

• Fix undefined metadata on the AI Transparency Center page
• Fix mobile styling

Production	Review app
https://about.gitlab.com/ai-transparency-center	https://ai-transparency-center-follow-up.about.gitlab-review.app/ai-transparency-center/

Step 2: Ensure that your changes comply with the following, where applicable:

• I, the Assignee, have run Axe tools on any updated pages, and fixed the relevant accessibility issues.
• These changes work on both Safari, Chrome, and Firefox.
• These changes have been reviewed for Visual Quality Assurance and Functional Quality Assurance on Mobile, Desktop, and Tablet.
• These changes work with our Google Analytics and SEO tools.
• These changes have been documented as expected.

Build Variables:

• Use Contentful Preview API