Add scroll up

[Diya-od]

Description

Added a Scroll-to-Top button on the leaderboard page to improve navigation and user experience. Users can now quickly return to the top of the page after scrolling through the leaderboard.

Linked Issue

Fixes #89

Changes Made

-Added a Scroll-to-Top button to the leaderboard page.
-Implemented smooth scrolling behavior when the button is clicked.
Configured the button to appear only after the user scrolls down a certain distance.
-Styled the button to match the existing UI design.

Type of Change

• [ x] Bug fix
• [ x] New feature
• UI/Visual update
• Documentation update
• Refactor

Testing

• [ x] Tested locally
• [ x] Tested on mobile viewport (if applicable)
• [ x] No console errors introduced

Checklist

• [ x] My code follows the project's coding style
• [ x] I have formatted my code locally using Prettier
• [x ] I have performed a self-review of my code
• [x ] My changes generate no new warnings or errors
• I have updated documentation if required
• [x ] I have linked the relevant issue

Screenshots / Screen Recording

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[jagdish-15]

I had originally intended this feature to remain primarily mobile-focused, as I had mentioned in the issue as well, since pagination already keeps the desktop page length relatively manageable.

Right now the scroll-to-top button is also visible on larger desktop layouts, which is not really needed.

Could you please update the implementation so the button is limited to smaller/mobile screen sizes?