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/objectWithoutProperties.js

@@ -0,0 +1,13 @@
+var objectWithoutPropertiesLoose = require("./objectWithoutPropertiesLoose.js");
+function _objectWithoutProperties(e, t) {
+  if (null == e) return {};
+  var o,
+    r,
+    i = objectWithoutPropertiesLoose(e, t);
+  if (Object.getOwnPropertySymbols) {
+    var n = Object.getOwnPropertySymbols(e);
+    for (r = 0; r < n.length; r++) o = n[r], -1 === t.indexOf(o) && {}.propertyIsEnumerable.call(e, o) && (i[o] = e[o]);
+  }
+  return i;
+}
+module.exports = _objectWithoutProperties, module.exports.__esModule = true, module.exports["default"] = module.exports;