Style : Add light and dark Home page UI design

What does this MR do?

This MR updates the Home page UI with a complete modern design refresh and adds light/dark theme support.

Key improvements

• Applied a polished dark theme design across the Home page
• Added a light theme alternative matching the provided light-mode preview
• Implemented a theme toggle in the Navbar
• Updated Home sections:
  • Hero
  • Summer of AI card
  • Goals
  • Initiatives
  • Impact dashboard
  • Contributor highlights
  • Roadmap
• Improved visual hierarchy, spacing, and readability
• Added consistent card styling, hover effects, and background textures

Why this change?

• The existing Home UI needed better visual clarity and consistency
• Light mode was missing and is now supported without breaking dark mode
• Cards and sections now have stronger contrast and better spacing
• The theming system is now scalable and aligned with modern UI standards

Checklist

• ✅ UI updated without changing content
• ✅ No functionality changes
• ✅ Dark theme preserved
• ✅ Light theme added safely
• ✅ Responsive design maintained
• ✅ Code follows project standards

Screenshots

Before

/ After