fix frontend invoke result handling

frontend/src/a2a.js

@@ -1,5 +1,11 @@
 export const CONFIG_URL = import.meta.env.DEV ? "/config.json" : "./config.json";
 
+export function unwrapInvokeResponse(payload) {
+  return payload && typeof payload === "object" && "result" in payload
+    ? payload.result
+    : payload;
+}
+
 export async function requestJson(url, init = {}) {
   const response = await fetch(url, { credentials: "same-origin", ...init });
   const text = await response.text();
@@ -51,11 +57,12 @@ export async function callSkill(config, skillName, args) {
     await requireSession(config);
   }
   try {
-    return await requestJson(`${config.endpoints.invoke}/${encodeURIComponent(skillName)}`, {
+    const payload = await requestJson(`${config.endpoints.invoke}/${encodeURIComponent(skillName)}`, {
       method: "POST",
       headers: { "content-type": "application/json" },
       body: JSON.stringify({ arguments: args }),
     });
+    return unwrapInvokeResponse(payload);
   } catch (err) {
     if (err.status === 401) {
       const target = signInUrl(config);