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/getIteratorMethod.js

@@ -0,0 +1,50 @@
+'use strict';
+
+var hasSymbols = require('has-symbols')();
+var GetIntrinsic = require('get-intrinsic');
+var callBound = require('call-bound');
+var isString = require('is-string');
+
+var $iterator = GetIntrinsic('%Symbol.iterator%', true);
+var $stringSlice = callBound('String.prototype.slice');
+var $String = GetIntrinsic('%String%');
+
+var IsArray = require('./IsArray');
+
+module.exports = function getIteratorMethod(ES, iterable) {
+	var usingIterator;
+	if (hasSymbols) {
+		usingIterator = ES.GetMethod(iterable, $iterator);
+	} else if (IsArray(iterable)) {
+		usingIterator = function () {
+			var i = -1;
+			var arr = this;
+			return {
+				next: function () {
+					i += 1;
+					return {
+						done: i >= arr.length,
+						value: arr[i]
+					};
+				}
+			};
+		};
+	} else if (isString(iterable)) {
+		usingIterator = function () {
+			var i = 0;
+			return {
+				next: function () {
+					var nextIndex = ES.AdvanceStringIndex($String(iterable), i, true);
+					var value = $stringSlice(iterable, i, nextIndex);
+					i = nextIndex;
+					var done = nextIndex > iterable.length;
+					return {
+						done: done,
+						value: done ? void undefined : value
+					};
+				}
+			};
+		};
+	}
+	return usingIterator;
+};