test(frontend): improve test coverage and update edge case handling

- Refactor tests to handle empty `model_params` in AgentTypeForm.
- Add return type annotations (`: never`) for throwing functions in ErrorBoundary tests.
- Mock `useAuth` in home page tests for consistent auth state handling.
- Update Header test to validate updated `/dashboard` link.

frontend/tests/components/layout/Header.test.tsx

@@ -124,7 +124,7 @@ describe('Header', () => {
       render(<Header />);
 
       const homeLink = screen.getByRole('link', { name: /home/i });
-      expect(homeLink).toHaveAttribute('href', '/');
+      expect(homeLink).toHaveAttribute('href', '/dashboard');
     });
 
     it('renders admin link for superusers', () => {