This pull request adds participant management features to the student activities app, including the ability to view, add, and remove participants from activities. It also introduces a suite of backend tests to ensure reliability. The changes span the backend API, frontend UI, and styling, making participant management user-friendly and robust.

Backend: Participant Management API

• Added a DELETE endpoint (/activities/{activity_name}/signup) to allow removing a participant from an activity, with proper error handling for not-found and not-registered cases.
• Improved the POST signup endpoint to prevent duplicate signups and provide clear error messages.

Frontend: Participant List and Removal

• Updated the activity cards to display a styled list of current participants, each with a "remove" button for easy participant removal.
• Implemented frontend logic to call the new DELETE API when a participant is removed, and to refresh the activities list after signup or removal. [1] [2]

Styling

• Added new CSS classes to style the participants section and remove button, ensuring a clean and user-friendly UI for participant management.

Backend: Data and Testing

• Expanded the initial set of activities with additional clubs and teams, each with participant lists.
• Introduced comprehensive backend tests for signup, duplicate signup, unregistering, and error cases, ensuring endpoint correctness and reliability.