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/call-bind-apply-helpers/index.js

@@ -0,0 +1,15 @@
+'use strict';
+
+var bind = require('function-bind');
+var $TypeError = require('es-errors/type');
+
+var $call = require('./functionCall');
+var $actualApply = require('./actualApply');
+
+/** @type {(args: [Function, thisArg?: unknown, ...args: unknown[]]) => Function} TODO FIXME, find a way to use import('.') */
+module.exports = function callBindBasic(args) {
+	if (args.length < 1 || typeof args[0] !== 'function') {
+		throw new $TypeError('a function is required');
+	}
+	return $actualApply(bind, $call, args);
+};