Fix Back to Top Button Positioning - Move to Right Side and Improve Visibility

[Channpreetk]

Fixed the back to top button positioning issue where it was appearing in the left corner of the footer, making it hard to see and access. The button is now properly positioned in the bottom-right corner with improved visibility.

Key Changes:
Repositioned from bottom-left to bottom-right corner (right: 30px)
Elevated position moved higher up (bottom: 100px) to avoid footer overlap
Enhanced styling with mint-green to lavender gradient matching site theme
Added hover effects with smooth transitions and color changes
Improved accessibility with better z-index and visibility above footer content

Result: The back to top button is now clearly visible in the bottom-right corner, positioned above the footer for optimal user accessibility and site navigation.

fixed #281

[github-actions]

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