fix(frontend): expose completed result state

frontend/src/App.jsx

@@ -154,7 +154,12 @@ export function App() {
           {error ? <p className="error" role="alert">{error}</p> : null}
         </section>
 
-        <section className="result-panel" data-testid="agent-result" aria-live="polite">
+        <section
+          className="result-panel"
+          data-testid="agent-result"
+          data-state={running ? "loading" : error ? "error" : result ? "success" : "idle"}
+          aria-live="polite"
+        >
           <div className="panel-heading">
             <p className="eyebrow">2. Live dashboard</p>
             <h2>{result ? result.summary : "Ready for the first run"}</h2>