Fix decorative image alt text in project cards (#176)

[Sarvan-Singh7]

This PR updates decorative project card images to use empty alt attributes (alt="") as recommended in issue #176.

Following W3C accessibility guidelines and maintainer feedback, decorative images inside links should not duplicate text that already appears in the card. Empty alt text makes screen readers skip the decorative image and prevents duplicate announcements.

Changes included:

• Set alt="" for decorative images in project cards
• Left meaningful icons/logos unchanged

This improves accessibility and aligns with the maintainer’s guidance. Thank you!