feat: Positive institutional disclaimer and contribution call (#302)

[mnietona]

Description

Following the UI PR split, this addresses Point 1 (Mandatory Institutional Disclaimer).

Resolves #302

Changes made based on your feedback:

• Positive Wording: Removed the "warning" vibe at the bottom of the landing page.
• Acknowledgments: Added a clear, welcoming banner that explicitly thanks the ULB CI and UrLab for providing and hosting the tool.
• Call to Action: Added a direct link to the GitHub repository to encourage students to get involved and contribute to the project.

Manual Testing:

• Verified the new layout looks clean on both desktop and mobile.
• Ensured the GitHub, UrLab, and UV links in the banner work correctly.

[C4ptainCrunch]

Awesome, thanks !