Added responsive footer with social and quick links

[erbhuwan]

Description

This PR adds a responsive footer to the project. The footer includes:

• Social Media Links: GitHub, LinkedIn, and Twitter icons with hover effects.
• Quick Links: Navigation to important pages including Home, Sorting, Graph, String, DP, About, Docs, and Contributors.
• Copyright & License: Centered at the bottom with current year and MIT license.
• Fully responsive layout and works in dark and light modes.

Screenshots

Type of Change

• New Feature / UI Component
• Responsive Design
• Dark/Light Mode Support

Checklist

• Social links are functional.
• Quick links navigate to respective pages.
• Footer is responsive across screen sizes.
• Dark/light mode support works correctly.

Related Issues

• Closes Fix Footer Links and Add Social Media #5