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/2025/CreateIteratorFromClosure.js

@@ -0,0 +1,51 @@
+'use strict';
+
+var $TypeError = require('es-errors/type');
+
+var GeneratorStart = require('./GeneratorStart');
+var IsArray = require('./IsArray');
+var IsCallable = require('./IsCallable');
+var OrdinaryObjectCreate = require('./OrdinaryObjectCreate');
+
+var every = require('../helpers/every');
+
+var SLOT = require('internal-slot');
+var safeConcat = require('safe-array-concat');
+var isObject = require('es-object-atoms/isObject');
+
+var isString = function isString(slot) {
+	return typeof slot === 'string';
+};
+
+// https://262.ecma-international.org/16.0/#sec-createiteratorfromclosure
+
+module.exports = function CreateIteratorFromClosure(closure, generatorBrand, generatorPrototype) {
+	if (!IsCallable(closure)) {
+		throw new $TypeError('`closure` must be a function');
+	}
+	if (typeof generatorBrand !== 'string') {
+		throw new $TypeError('`generatorBrand` must be a string');
+	}
+	if (!isObject(generatorPrototype)) {
+		throw new $TypeError('`generatorPrototype` must be an object');
+	}
+	var extraSlots = arguments.length > 3 ? arguments[3] : []; // step 2
+	if (arguments.length > 3) {
+		if (!IsArray(extraSlots) || !every(extraSlots, isString)) {
+			throw new $TypeError('`extraSlots` must be a List of String internal slot names');
+		}
+	}
+	var internalSlotsList = safeConcat(extraSlots, ['[[GeneratorContext]]', '[[GeneratorBrand]]', '[[GeneratorState]]']); // step 3
+	var generator = OrdinaryObjectCreate(generatorPrototype, internalSlotsList); // steps 4, 6
+	SLOT.set(generator, '[[GeneratorBrand]]', generatorBrand); // step 5
+	SLOT.set(generator, '[[GeneratorState]]', 'SUSPENDED-START'); // step 6
+
+	SLOT.assert(closure, '[[Sentinel]]'); // our userland slot
+	SLOT.set(generator, '[[Sentinel]]', SLOT.get(closure, '[[Sentinel]]')); // our userland slot
+	SLOT.assert(closure, '[[CloseIfAbrupt]]'); // our second userland slot
+	SLOT.set(generator, '[[CloseIfAbrupt]]', SLOT.get(closure, '[[CloseIfAbrupt]]')); // our second userland slot
+
+	GeneratorStart(generator, closure); // step 14
+
+	return generator; // step 16
+};