Add audiowidget endpoint: Blueprint renders audiowidget.tmpl, PaneCP fetches it on synthesis completion

static/api.js

@@ -44,3 +44,12 @@ export async function fetchStatus(credentials) {
     if (!res.ok) throw new Error(`${res.status} ${res.statusText}`);
     return res.json();
 }
+
+export async function fetchAudioWidget(resultUrl, errors) {
+    const params = new URLSearchParams();
+    if (resultUrl) params.set('result_url', resultUrl);
+    if (errors)    params.set('errors', errors);
+    const res = await fetch(`${U.audiowidget}?${params}`);
+    if (!res.ok || res.status === 204) return '';
+    return res.text();
+}