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>,

frontend/tests/components/agents/AgentTypeForm.test.tsx

@@ -549,14 +549,14 @@ describe('AgentTypeForm', () => {
     });
   });
 
-  describe('Null Model Params Handling', () => {
+  describe('Empty Model Params Handling', () => {
-    it('handles null model_params gracefully', () => {
+    it('handles empty model_params gracefully', () => {
-      const agentTypeWithNullParams: AgentTypeResponse = {
+      const agentTypeWithEmptyParams: AgentTypeResponse = {
         ...mockAgentType,
-        model_params: null,
+        model_params: {},
       };
 
-      render(<AgentTypeForm {...defaultProps} agentType={agentTypeWithNullParams} />);
+      render(<AgentTypeForm {...defaultProps} agentType={agentTypeWithEmptyParams} />);
 
       // Should render without errors
       expect(screen.getByText('Edit Agent Type')).toBeInTheDocument();

frontend/tests/components/common/ErrorBoundary.test.tsx

@@ -248,7 +248,7 @@ describe('ErrorBoundary', () => {
 
   describe('error without message', () => {
     it('handles error with null message gracefully', () => {
-      function ThrowNullError() {
+      function ThrowNullError(): never {
         const error = new Error();
         error.message = '';
         throw error;
@@ -338,7 +338,7 @@ describe('ErrorBoundary', () => {
 
   describe('edge cases', () => {
     it('handles deeply nested errors', () => {
-      function DeepChild() {
+      function DeepChild(): never {
         throw new Error('Deep error');
       }
 
@@ -377,7 +377,7 @@ describe('ErrorBoundary', () => {
     });
 
     it('allows nested error boundaries', () => {
-      function InnerThrowing() {
+      function InnerThrowing(): never {
         throw new Error('Inner error');
       }
 

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', () => {