Add Dark Mode Theme

[MasterAffan]

Description:
Implement dark mode theme throughout the Flutter app with theme switching functionality.

Tasks:

• Create dark theme color palette
• Implement theme switching logic
• Add theme toggle in settings
• Ensure all widgets support dark mode
• Persist theme preference
• Test theme switching across all screens

Acceptance Criteria:

• Dark mode works on all screens
• Theme preference persists across app restarts
• Smooth theme switching without flicker
• All UI elements properly themed

[Zaki-Mohd]

I’d like to take this issue. Please assign it to me under hacktoberfest!

[AKRITI-ENG]

I'd like to work on this issue for Hacktoberfest. Could you please assign it to me?

[MasterAffan]

@Zaki-Mohd assigned to you

[MasterAffan]

@AKRITI-ENG sorry its fcfs you can work on other issues

[Zaki-Mohd]

@MasterAffan please add a label hacktoberfest-accepted