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/2023/GetIteratorFromMethod.js

@@ -0,0 +1,28 @@
+'use strict';
+
+var $TypeError = require('es-errors/type');
+var isObject = require('es-object-atoms/isObject');
+
+var Call = require('./Call');
+var GetV = require('./GetV');
+var IsCallable = require('./IsCallable');
+
+// https://262.ecma-international.org/14.0/#sec-getiteratorfrommethod
+
+module.exports = function GetIteratorFromMethod(obj, method) {
+	if (!IsCallable(method)) {
+		throw new $TypeError('method must be a function');
+	}
+
+	var iterator = Call(method, obj); // step 1
+	if (!isObject(iterator)) {
+		throw new $TypeError('iterator must return an object'); // step 2
+	}
+
+	var nextMethod = GetV(iterator, 'next'); // step 3
+	return { // steps 4-5
+		'[[Iterator]]': iterator,
+		'[[NextMethod]]': nextMethod,
+		'[[Done]]': false
+	};
+};