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/app/page.test.tsx

@@ -55,6 +55,15 @@ jest.mock('@/lib/api/hooks/useAuth', () => ({
   })),
 }));
 
+// Mock AuthContext - Home page uses useAuth to check if user is authenticated
+jest.mock('@/lib/auth/AuthContext', () => ({
+  useAuth: jest.fn(() => ({
+    isAuthenticated: false,
+    isLoading: false,
+    user: null,
+  })),
+}));
+
 // Mock Theme components
 jest.mock('@/components/theme', () => ({
   ThemeToggle: () => <div data-testid="theme-toggle">Theme Toggle</div>,