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/define-properties/index.js

@@ -0,0 +1,47 @@
+'use strict';
+
+var keys = require('object-keys');
+var hasSymbols = typeof Symbol === 'function' && typeof Symbol('foo') === 'symbol';
+
+var toStr = Object.prototype.toString;
+var concat = Array.prototype.concat;
+var defineDataProperty = require('define-data-property');
+
+var isFunction = function (fn) {
+	return typeof fn === 'function' && toStr.call(fn) === '[object Function]';
+};
+
+var supportsDescriptors = require('has-property-descriptors')();
+
+var defineProperty = function (object, name, value, predicate) {
+	if (name in object) {
+		if (predicate === true) {
+			if (object[name] === value) {
+				return;
+			}
+		} else if (!isFunction(predicate) || !predicate()) {
+			return;
+		}
+	}
+
+	if (supportsDescriptors) {
+		defineDataProperty(object, name, value, true);
+	} else {
+		defineDataProperty(object, name, value);
+	}
+};
+
+var defineProperties = function (object, map) {
+	var predicates = arguments.length > 2 ? arguments[2] : {};
+	var props = keys(map);
+	if (hasSymbols) {
+		props = concat.call(props, Object.getOwnPropertySymbols(map));
+	}
+	for (var i = 0; i < props.length; i += 1) {
+		defineProperty(object, props[i], map[props[i]], predicates[props[i]]);
+	}
+};
+
+defineProperties.supportsDescriptors = !!supportsDescriptors;
+
+module.exports = defineProperties;