Hackathon experience improvement: responsive hackathon group layout

When looking at the hackathon landing page on viewports less than 1024px, each hackathon group section flows in a row without `inline-size` applied to the card grid.

<img width="849" height="699" alt="Image" src="https://github.com/user-attachments/assets/0f0c268b-fa3a-4fc6-8b28-a7a73be8a9dc" />