Add Dark Mode Toggle

[AeleSahithi]

Adding a dark mode toggle will enhance accessibility and improve user experience by offering a visually comfortable alternative.

Suggested Solution:

UI: Add a toggle switch in the top-right corner of the header.
Theme Settings: Implement CSS variables for colors, adjusting them to provide a darker theme when toggled.
Persistence: Use localStorage to remember the user's theme choice between sessions.
Acceptance Criteria:

Dark mode toggle should appear in the header.
Switching themes should apply consistent styles across all UI components.
The selected theme (light or dark) should persist even after refreshing or closing the app.
Additional Notes:

Consider testing on both desktop and mobile layouts.
Reference Material Design color guidelines for dark themes if needed.