[Feature✨]: Implement Dark Theme Feature in HireHub

[AnushkaChouhan25]

Is your feature request related to a problem? Please describe.
I propose adding a dark theme feature to the HireHub project. This will provide users with an alternative viewing option, improving accessibility and user experience, especially in low-light environments.

Describe the solution you'd like

• Create a dark theme style guide to define colors, backgrounds, and typography for the dark mode.
• Implement a toggle switch or button that allows users to switch between light and dark themes seamlessly.
• Ensure all components, including text, icons, and backgrounds, are adjusted to maintain readability and aesthetic consistency in dark mode.

Deadline to complete - within one day