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/set.js

@@ -0,0 +1,22 @@
+import superPropBase from "./superPropBase.js";
+import defineProperty from "./defineProperty.js";
+function set(e, r, t, o) {
+  return set = "undefined" != typeof Reflect && Reflect.set ? Reflect.set : function (e, r, t, o) {
+    var f,
+      i = superPropBase(e, r);
+    if (i) {
+      if ((f = Object.getOwnPropertyDescriptor(i, r)).set) return f.set.call(o, t), !0;
+      if (!f.writable) return !1;
+    }
+    if (f = Object.getOwnPropertyDescriptor(o, r)) {
+      if (!f.writable) return !1;
+      f.value = t, Object.defineProperty(o, r, f);
+    } else defineProperty(o, r, t);
+    return !0;
+  }, set(e, r, t, o);
+}
+function _set(e, r, t, o, f) {
+  if (!set(e, r, t, o || e) && f) throw new TypeError("failed to set property");
+  return t;
+}
+export { _set as default };