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/backend/src/modules/complex/handlers/accept-complex-invitations.handler.ts

@@ -0,0 +1,27 @@
+import {
+  ComplexMembersError,
+  acceptComplexInvitations,
+} from '@/modules/complex/services/complex-members.service';
+import type { AppContext } from '@/types/hono';
+import type { AcceptComplexInvitationsInput } from '@repo/api-contract';
+
+export async function acceptComplexInvitationsHandler(c: AppContext) {
+  const user = c.get('user');
+  const payload = c.req.valid('json' as never) as AcceptComplexInvitationsInput;
+
+  try {
+    const result = await acceptComplexInvitations(user.id, user.email, payload);
+    return c.json(result);
+  } catch (error) {
+    if (error instanceof ComplexMembersError) {
+      return c.json(
+        { message: error.message },
+        {
+          status: error.status,
+        }
+      );
+    }
+
+    throw error;
+  }
+}