Add Dark/Light Theme Toggle Functionality

[madhulatha777]

The current UI does not support theme switching, which can limit accessibility and user preference. I would like to implement a Dark and Light mode toggle button that allows users to switch between themes seamlessly.

Key features of this enhancement:

A toggle button (icon-based or switch) in the navbar or header

Persistent theme preference using localStorage

Smooth transition between themes

Fully responsive and accessible design updates for both modes

This addition will improve the user experience and align the project with modern UI standards.

@4darsh-Dev Assign this task to me and Add GSSoc labels.

[4darsh-Dev]

@madhulatha777 assigned to you
go through contriubting guidelines and /docs on website.

[alizahh-7]

@4darsh-Dev I would like to contibute to this issue.