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/2024/IteratorStepValue.js

@@ -0,0 +1,49 @@
+'use strict';
+
+var $TypeError = require('es-errors/type');
+
+var Get = require('./Get');
+var IteratorComplete = require('./IteratorComplete');
+var IteratorNext = require('./IteratorNext');
+
+var isIteratorRecord = require('../helpers/records/iterator-record');
+
+// https://262.ecma-international.org/15.0/#sec-iteratorstepvalue
+
+module.exports = function IteratorStepValue(iteratorRecord) {
+	if (!isIteratorRecord(iteratorRecord)) {
+		throw new $TypeError('Assertion failed: `iteratorRecord` must be an Iterator Record');
+	}
+	/* eslint no-param-reassign: 0 */
+
+	var result;
+	try {
+		result = IteratorNext(iteratorRecord); // step 1
+	} catch (e) { // step 2
+		iteratorRecord['[[Done]]'] = true; // step 2.a
+		throw e; // step 2.b
+	}
+
+	var done;
+	try {
+		done = IteratorComplete(result); // step 4
+	} catch (e) { // step 5
+		iteratorRecord['[[Done]]'] = true; // step 5.a
+		throw e; // step 5.b
+	}
+
+	if (done) { // step 7
+		iteratorRecord['[[Done]]'] = true; // step 7.a
+		return 'DONE'; // step 7.b
+	}
+
+	var value;
+	try {
+		value = Get(result, 'value'); // step 8
+	} catch (e) { // step 9
+		iteratorRecord['[[Done]]'] = true; // step 9.a
+		throw e; // step 10
+	}
+
+	return value; // step 10
+};