Description: Create a DELETE route in notification.controller.ts and the corresponding service method in notification.service.ts to delete a notification from the database. This will be used when a user clears a notification. This ticket will also involve making new tests in notification.service.test.ts to test this delete method

Acceptance Criteria:

• A new DELETE route (@delete) exists in backend/src/notification/notification.controller.ts
• A corresponding function is implemented in backend/src/notification/notification.service.ts to handle notification deletion by id.
• Route successfully deletes the notification record from the database.
• If the notification does not exist, the route returns a meaningful error
• Unit tests exist to confirm:
  • Successful deletion of a valid notification ID.
  • Proper error handling when a notification does not exist.
• Code is clean, consistent with existing backend patterns, and includes comments where needed.