Add sync error logging, extend error flash, fix unload saves

- Log workforce sync errors to backend stdout so they appear in docker logs
- Extend error flash from 5s to 15s so errors are readable
- Replace sendBeacon (POST-only) with keepalive fetch (PUT) on unload —
  sendBeacon was hitting 404s on all three unload saves

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/node_modules/@babel/runtime/helpers/esm/defineEnumerableProperties.js

@@ -0,0 +1,12 @@
+function _defineEnumerableProperties(e, r) {
+  for (var t in r) {
+    var n = r[t];
+    n.configurable = n.enumerable = !0, "value" in n && (n.writable = !0), Object.defineProperty(e, t, n);
+  }
+  if (Object.getOwnPropertySymbols) for (var a = Object.getOwnPropertySymbols(r), b = 0; b < a.length; b++) {
+    var i = a[b];
+    (n = r[i]).configurable = n.enumerable = !0, "value" in n && (n.writable = !0), Object.defineProperty(e, i, n);
+  }
+  return e;
+}
+export { _defineEnumerableProperties as default };