Add Notification System with Toast Messages

[Mutti499]

This PR implements a notification system using toast messages that appear in the top-right corner of the application.

Key Features:

• Toast notifications with fade animations
• Automatic dismissal after 5 seconds
• Close button for manual dismissal
• Responsive design that works across different screen sizes

Technical Changes:

• Added NotificationCenter component for managing toast messages
• Implemented event-based notification system for cross-component communication
• Added fade-in/fade-out animations using CSS transitions
• Responsive styling for different viewport sizes

Testing:

• In pages where the alert is used, functions should be retried and notification logic should be observed.

Additions:

• Logout button location fixed.
• Responsiveness to the top contributors added.
• LLM rejection got more explicit message.