feat: add age verification modal to homepage

[dinahmaccodes]

Description

• Implemented an age verification modal that appears on the first visit to the site.
• Modal blocks all site interaction until the user enters their full name and verifies they are 18+.
• Modal is fully responsive and styled to match the site’s purple theme.
• User’s verification is stored in localStorage, so the modal only pops up once per browser/profile.
• Includes links to terms of service and privacy policy.

Closes #10

@martinvibes

[martinvibes]

looking good to me!