Implement Responsive UI with Header/Footer (#68)

[2400031665]

📌 Summary

Implemented responsive UI with header/footer (#68).

🔄 Changes Made

• Added semantic header, navigation, and footer components.
• Implemented responsive layout using Flexbox and CSS variables.
• Introduced dark mode toggle with improved color palette and smooth transitions.
• Created navigation tabs for Tasks, Progress, and Timer pages.
• Enhanced task management (add, edit, delete, toggle completion).
• Improved real-time progress tracking with percentage display.
• Refined timer functionality with start/stop controls and formatted output.
• Added sticky footer with copyright and GitHub profile link.
• Updated README Key Features section to reflect new UI/UX enhancements.

✅ Checklist

• Branch name follows convention (feature/responsive-ui-header-footer)
• Commit message references issue (Implement Responsive UI with Header/Footer #68)
• Code follows project’s clean, minimalist style
• README updated with new features
• Tested responsiveness on mobile, tablet, and desktop

[2400031665]

HIi @JIYAJAIN30 It's been nearly 2 weeks that I made this PR. I would kindly request you to verify the issue and the PR. I would be grateful for your response. I am Gssoc'26 contributor. Please do consider my request. Thank you so much.