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/GetSetRecord.js

@@ -0,0 +1,64 @@
+'use strict';
+
+var $RangeError = require('es-errors/range');
+var $TypeError = require('es-errors/type');
+
+var Get = require('./Get');
+var IsCallable = require('./IsCallable');
+var ToIntegerOrInfinity = require('./ToIntegerOrInfinity');
+var ToNumber = require('./ToNumber');
+
+var isNaN = require('..//helpers/isNaN');
+var isObject = require('es-object-atoms/isObject');
+
+var callBind = require('call-bind');
+var isSet = require('is-set');
+var stopIterationIterator = require('stop-iteration-iterator');
+
+// https://262.ecma-international.org/16.0/#sec-getsetrecord
+
+module.exports = function GetSetRecord(obj) {
+	if (!isObject(obj)) {
+		throw new $TypeError('obj is not an Object'); // step 1
+	}
+
+	var rawSize = Get(obj, 'size'); // step 2
+
+	var numSize = ToNumber(rawSize); // step 3
+
+	//  4. NOTE: If rawSize is undefined, then numSize will be NaN.
+	if (isNaN(numSize)) {
+		throw new $TypeError('`size` is not a non-NaN Number'); // step 5
+	}
+
+	var intSize = ToIntegerOrInfinity(numSize); // step 6
+
+	if (intSize < 0) {
+		throw new $RangeError('set size must be non-negative'); // step 7
+	}
+
+	var has = Get(obj, 'has'); // step 8
+
+	if (!IsCallable(has)) {
+		throw new $TypeError('has is not a function'); // step 9
+	}
+
+	var keys = Get(obj, 'keys'); // step 10
+	if (!IsCallable(keys)) {
+		throw new $TypeError('keys is not a function'); // step 11
+	}
+	/* globals StopIteration: false */
+	if (isSet(obj) && typeof StopIteration === 'object') {
+		var boundKeys = callBind(keys);
+		keys = function keys() { // eslint-disable-line no-shadow
+			return stopIterationIterator(boundKeys(this));
+		};
+	}
+
+	return {
+		'[[SetObject]]': obj,
+		'[[Size]]': intSize,
+		'[[Has]]': has,
+		'[[Keys]]': keys
+	}; // step 12
+};