Create Export to CSV Feature

[swaparup36]

Allow users to export their assignments and grades to CSV format for use in spreadsheets.

Task:

• Add export functionality using Python's csv module
• Create separate exports for assignments and grades
• Add CLI command for export
• Allow user to specify output filename

Expected Usage:

python main.py export assignments --output my_assignments.csv
python main.py export grades --output my_grades.csv

[TitanX311]

i want to work on this issue. assign it to me.