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/index.js

@@ -0,0 +1,24 @@
+'use strict';
+
+var setFunctionLength = require('set-function-length');
+
+var $defineProperty = require('es-define-property');
+
+var callBindBasic = require('call-bind-apply-helpers');
+var applyBind = require('call-bind-apply-helpers/applyBind');
+
+module.exports = function callBind(originalFunction) {
+	var func = callBindBasic(arguments);
+	var adjustedLength = 1 + originalFunction.length - (arguments.length - 1);
+	return setFunctionLength(
+		func,
+		adjustedLength > 0 ? adjustedLength : 0,
+		true
+	);
+};
+
+if ($defineProperty) {
+	$defineProperty(module.exports, 'apply', { value: applyBind });
+} else {
+	module.exports.apply = applyBind;
+}