Add source code link for Leeroo submission

[alirezamshi]

Hi MLE-bench team!

We're excited to share that we've open-sourced the framework of Leeroo submission.

This PR updates the Leeroo leaderboard entry to include the open-source repository link.

Changes

• Updated Leeroo agent link to point to the source code repository: https://github.com/Leeroo-AI/kapso
• Marked "Source Code Available" as ✓

KAPSO is now publicly available under MIT license.

Best,
Leeroo team

[alirezamshi]

@joe-needham