Add Export to CSV Feature

[Sangiwe]

It would be beneficial to have an export to CSV feature that allows users to download their grade data in a CSV format. This feature would help users easily share or analyze their grades outside of the application.

• Add an "Export to CSV" button in the user dashboard.
• Implement a function to convert grade data into CSV format.
• Provide options to export all grades or filtered views.
• Consider compatibility with various spreadsheet applications (e.g., Excel, Google Sheets).