feat: add complex user invitation and management features

- Implemented complex member and invitation schemas using Zod for validation.
- Created new API endpoints for inviting, accepting, revoking, and canceling complex user invitations.
- Developed handlers for managing complex users, including listing, inviting, revoking, and canceling invitations.
- Added frontend components for displaying and managing complex users and invitations.
- Introduced session storage management for pending invitations.
- Integrated Gravatar for user avatars based on email.
- Created database migration for complex invitations table.

apps/frontend/src/routes/auth-callback.tsx

@@ -1,5 +1,6 @@
 import { apiClient } from '@/lib/api-client';
 import { useAuth } from '@/lib/auth';
+import { acceptStoredPendingInvite } from '@/lib/invitations';
 import { createFileRoute, useNavigate } from '@tanstack/react-router';
 import { useEffect } from 'react';
 
@@ -15,6 +16,7 @@ function AuthCallbackPage() {
       }
 
       try {
+        await acceptStoredPendingInvite(apiClient.complexes.acceptPendingInvitations);
         const complexes = await apiClient.complexes.listMine();
 
         if (complexes.length === 1) {