feat: Add a Jump to top button for Terms page

[DimondKudzai]

This PR introduces a small, self-contained UI component (JumpToTop) placed in the src/components/ui directory. It enhances the user experience on long pages (like Terms of Use) by allowing users to quickly scroll back to the top.

• Added JumpToTop component with scroll visibility logic
• Used SCSS for styling, consistent with existing design patterns
• Modular and non-intrusive — no core logic modified
• Imported via @ui and reused cleanly in the Terms.tsx page

This is a minor usability improvement and aligns with the modular UI structure of the project.

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