fix(ui): stop New Agent infinite render loop in AgentConfigForm

Creating an agent rendered a blank page (now a "Maximum update depth
exceeded" error card). `triggerTestEnvironment` was rebuilt every render
because `runEnvironmentTest` depends on the `useMutation` result object,
which gets a fresh identity each render. The `onTestActionChange` effect
then fired every render and pushed a new function into the parent's
state (setTestAgentAction), forcing another render — an infinite loop.

Hold the latest trigger behavior in a ref and hand the parent a stable
callback so the effect runs once. The Test Agent button still invokes the
current logic via the ref.

ui/src/components/AgentConfigForm.tsx

@@ -550,10 +550,21 @@ export function AgentConfigForm(props: AgentConfigFormProps) {
       setTestActionPending(false);
     }
   }, [selectedCompanyId, isCreate, isDirty, handleSave, testEnvironment]);
-  const triggerTestEnvironment = useCallback(() => {
-    if (testEnvironmentDisabled) return;
-    void runEnvironmentTest().catch(() => undefined);
+  // `runEnvironmentTest` (and `testEnvironmentDisabled`) change identity on every
+  // render because `useMutation` returns a fresh result object each time. Hold the
+  // latest behavior in a ref so the trigger handed to the parent stays referentially
+  // stable — otherwise the `onTestActionChange` effect below re-runs every render,
+  // pushing a new function into parent state and causing an infinite update loop.
+  const triggerRef = useRef<() => void>(() => {});
+  useEffect(() => {
+    triggerRef.current = () => {
+      if (testEnvironmentDisabled) return;
+      void runEnvironmentTest().catch(() => undefined);
+    };
   }, [runEnvironmentTest, testEnvironmentDisabled]);
+  const triggerTestEnvironment = useCallback(() => {
+    triggerRef.current();
+  }, []);
 
   useEffect(() => {
     if (!showAdapterTestEnvironmentButton || !props.onTestActionChange) return;