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/2016/CompletePropertyDescriptor.js

@@ -0,0 +1,43 @@
+'use strict';
+
+var $TypeError = require('es-errors/type');
+
+var hasOwn = require('hasown');
+
+var IsDataDescriptor = require('./IsDataDescriptor');
+var IsGenericDescriptor = require('./IsGenericDescriptor');
+
+var isPropertyDescriptor = require('../helpers/records/property-descriptor');
+
+// https://262.ecma-international.org/6.0/#sec-completepropertydescriptor
+
+module.exports = function CompletePropertyDescriptor(Desc) {
+	if (!isPropertyDescriptor(Desc)) {
+		throw new $TypeError('Assertion failed: `Desc` must be a Property Descriptor');
+	}
+
+	/* eslint no-param-reassign: 0 */
+
+	if (IsGenericDescriptor(Desc) || IsDataDescriptor(Desc)) {
+		if (!hasOwn(Desc, '[[Value]]')) {
+			Desc['[[Value]]'] = void 0;
+		}
+		if (!hasOwn(Desc, '[[Writable]]')) {
+			Desc['[[Writable]]'] = false;
+		}
+	} else {
+		if (!hasOwn(Desc, '[[Get]]')) {
+			Desc['[[Get]]'] = void 0;
+		}
+		if (!hasOwn(Desc, '[[Set]]')) {
+			Desc['[[Set]]'] = void 0;
+		}
+	}
+	if (!hasOwn(Desc, '[[Enumerable]]')) {
+		Desc['[[Enumerable]]'] = false;
+	}
+	if (!hasOwn(Desc, '[[Configurable]]')) {
+		Desc['[[Configurable]]'] = false;
+	}
+	return Desc;
+};