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/asyncToGenerator.js

@@ -0,0 +1,26 @@
+function asyncGeneratorStep(n, t, e, r, o, a, c) {
+  try {
+    var i = n[a](c),
+      u = i.value;
+  } catch (n) {
+    return void e(n);
+  }
+  i.done ? t(u) : Promise.resolve(u).then(r, o);
+}
+function _asyncToGenerator(n) {
+  return function () {
+    var t = this,
+      e = arguments;
+    return new Promise(function (r, o) {
+      var a = n.apply(t, e);
+      function _next(n) {
+        asyncGeneratorStep(a, r, o, _next, _throw, "next", n);
+      }
+      function _throw(n) {
+        asyncGeneratorStep(a, r, o, _next, _throw, "throw", n);
+      }
+      _next(void 0);
+    });
+  };
+}
+module.exports = _asyncToGenerator, module.exports.__esModule = true, module.exports["default"] = module.exports;