fix: add displayName to MockLink in UserDropdown test

Fixes ESLint react/display-name error by adding displayName
property to the MockLink component in the jest mock.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

__tests__/components/UserDropdown.test.tsx

@@ -9,9 +9,11 @@ import { UserDropdown } from '@/components/UserDropdown';
 
 // Mock next/link
 jest.mock('next/link', () => {
-  return ({ children, href }: { children: React.ReactNode; href: string }) => (
+  const MockLink = ({ children, href }: { children: React.ReactNode; href: string }) => (
     <a href={href}>{children}</a>
   );
+  MockLink.displayName = 'MockLink';
+  return MockLink;
 });
 
 describe('UserDropdown', () => {