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/es-abstract/helpers/DefineOwnProperty.js

@@ -0,0 +1,53 @@
+'use strict';
+
+var hasPropertyDescriptors = require('has-property-descriptors');
+
+var $defineProperty = require('es-define-property');
+
+var hasArrayLengthDefineBug = hasPropertyDescriptors.hasArrayLengthDefineBug();
+
+// eslint-disable-next-line global-require
+var isArray = hasArrayLengthDefineBug && require('../helpers/IsArray');
+
+var callBound = require('call-bound');
+
+var $isEnumerable = callBound('Object.prototype.propertyIsEnumerable');
+
+// eslint-disable-next-line max-params
+module.exports = function DefineOwnProperty(IsDataDescriptor, SameValue, FromPropertyDescriptor, O, P, desc) {
+	if (!$defineProperty) {
+		if (!IsDataDescriptor(desc)) {
+			// ES3 does not support getters/setters
+			return false;
+		}
+		if (!desc['[[Configurable]]'] || !desc['[[Writable]]']) {
+			return false;
+		}
+
+		// fallback for ES3
+		if (P in O && $isEnumerable(O, P) !== !!desc['[[Enumerable]]']) {
+			// a non-enumerable existing property
+			return false;
+		}
+
+		// property does not exist at all, or exists but is enumerable
+		var V = desc['[[Value]]'];
+		// eslint-disable-next-line no-param-reassign
+		O[P] = V; // will use [[Define]]
+		return SameValue(O[P], V);
+	}
+	if (
+		hasArrayLengthDefineBug
+		&& P === 'length'
+		&& '[[Value]]' in desc
+		&& isArray(O)
+		&& O.length !== desc['[[Value]]']
+	) {
+		// eslint-disable-next-line no-param-reassign
+		O.length = desc['[[Value]]'];
+		return O.length === desc['[[Value]]'];
+	}
+
+	$defineProperty(O, P, FromPropertyDescriptor(desc));
+	return true;
+};