feat: add new Tailwind-based style and visual improvements to site (#442)

- Introduced Tailwind CSS via CDN for rapid prototyping and modern utility classes
- Added custom theme colors (brand, primary, accent) to Tailwind config
- Implemented new topbar, header, and background decorations for a fresh look
- Enhanced theme card selection visuals and added a prominent GitHub "Contrib" ribbon
- Improved responsive layout and accessibility for navigation and call-to-action buttons
- Updated contributors section to dynamically load GitHub members
- Refactored and modernized overall HTML structure and CSS for maintainability

This update brings a modern, visually appealing, and more maintainable style to the Vim Bootstrap site, leveraging Tailwind CSS and improved UX patterns.

Signed-off-by: Avelino <31996+avelino@users.noreply.github.com>

Author: avelino