fix(ui): prevent destructure crash in Auto Router test connection

prepareModelAddRequest returns an empty array for auto router forms
(no model_mappings field), causing result[0] to be undefined when
destructuring litellmParamsObj.

Two fixes:
- Guard against empty result array in model_connection_test.tsx
- Pass properly constructed model_mappings from the auto router tab
  so test connection actually works for auto routers

ui/litellm-dashboard/src/components/add_model/add_auto_router_tab.tsx

@@ -436,11 +436,19 @@ const AddAutoRouterTab: React.FC<AddAutoRouterTabProps> = ({ form, handleOk, acc
         ]}
         width={700}
       >
-        {/* Only render the ConnectionErrorDisplay when modal is visible and we have a test ID */}
         {isResultModalVisible && (
           <ConnectionErrorDisplay
             key={connectionTestId}
-            formValues={form.getFieldsValue()}
+            formValues={{
+              ...form.getFieldsValue(),
+              custom_llm_provider: "auto_router",
+              model_mappings: [{
+                public_name: form.getFieldValue("auto_router_name") || "auto_router",
+                litellm_model: routerType === "complexity"
+                  ? "auto_router/complexity_router"
+                  : `auto_router/${form.getFieldValue("auto_router_name") || "auto_router"}`,
+              }],
+            }}
             accessToken={accessToken}
             testMode="chat"
             modelName={form.getFieldValue("auto_router_name")}

ui/litellm-dashboard/src/components/add_model/model_connection_test.tsx

@@ -45,7 +45,7 @@ const ModelConnectionTest: React.FC<ModelConnectionTestProps> = ({
       console.log("Testing connection with form values:", formValues);
       const result = await prepareModelAddRequest(formValues, accessToken, null);
 
-      if (!result) {
+      if (!result || result.length === 0) {
         console.log("No result from prepareModelAddRequest");
         setError("Failed to prepare model data. Please check your form inputs.");
         setIsSuccess(false);