feat: implement scroll to top button and fix stray code in index.html

[Chirag1724]

Description

• Implemented a floating "Scroll to Top" button that appears after scrolling 300px.
• Created programmatic button injection in main.js for global availability.
• Added premium-themed CSS transitions and hover effects in styles.css.
• Fixed a bug in index.html where raw JavaScript code was rendering below the footer.
• Cleaned up duplicate comments and restored correct AOS initialization in index.html.

Related Issue

Closes #213

Screenshot

Verification

• Verified button visibility on scroll.
• Verified smooth scroll-to-top functionality.
• Confirmed that stray code below the footer is removed.

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