feat: add group waitlist functionality

- Introduced GroupWaitlistEntry model in Prisma schema to manage waitlisted users for groups.
- Implemented API route to add users to the group waitlist with validation.
- Enhanced attendee creation logic to handle group capacity and waitlisting scenarios.
- Added new problem builders for handling waitlist-related errors.
- Updated frontend to support waitlist interactions, including modals for capacity warnings.
- Created tests for waitlist functionality, ensuring proper handling of full groups and existing waitlist entries.

apps/backend/src/modules/groups/routes.ts

@@ -1,4 +1,5 @@
 import { Hono } from 'hono';
+import addToGroupWaitlistRoute from '../attendees/features/add-to-waitlist/route';
 import bulkCreateAttendeesRoute from '../attendees/features/bulk-create/route';
 import createAttendeeRoute from '../attendees/features/create/route';
 import createFromOrganizationRoute from './features/create-from-organization/route';
@@ -16,5 +17,6 @@ routes.route('/', listAttendeesRoute);
 routes.route('/', createAttendeeRoute);
 routes.route('/', bulkCreateAttendeesRoute);
 routes.route('/', getByIdRoute);
+routes.route('/', addToGroupWaitlistRoute);
 
 export default routes;