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/agents/AgentTypeForm.test.tsx

@@ -549,14 +549,14 @@ describe('AgentTypeForm', () => {
     });
   });
 
-  describe('Null Model Params Handling', () => {
-    it('handles null model_params gracefully', () => {
-      const agentTypeWithNullParams: AgentTypeResponse = {
+  describe('Empty Model Params Handling', () => {
+    it('handles empty model_params gracefully', () => {
+      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();