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/2021/OrdinaryCreateFromConstructor.js

@@ -0,0 +1,20 @@
+'use strict';
+
+var GetIntrinsic = require('get-intrinsic');
+var $TypeError = require('es-errors/type');
+
+var GetPrototypeFromConstructor = require('./GetPrototypeFromConstructor');
+var IsArray = require('./IsArray');
+var OrdinaryObjectCreate = require('./OrdinaryObjectCreate');
+
+// https://262.ecma-international.org/6.0/#sec-ordinarycreatefromconstructor
+
+module.exports = function OrdinaryCreateFromConstructor(constructor, intrinsicDefaultProto) {
+	GetIntrinsic(intrinsicDefaultProto); // throws if not a valid intrinsic
+	var proto = GetPrototypeFromConstructor(constructor, intrinsicDefaultProto);
+	var slots = arguments.length < 3 ? [] : arguments[2];
+	if (!IsArray(slots)) {
+		throw new $TypeError('Assertion failed: if provided, `internalSlotsList` must be a List');
+	}
+	return OrdinaryObjectCreate(proto, slots);
+};