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/GetArrayBufferMaxByteLengthOption.js

@@ -0,0 +1,22 @@
+'use strict';
+
+var isObject = require('es-object-atoms/isObject');
+
+var Get = require('./Get');
+var ToIndex = require('./ToIndex');
+
+// https://262.ecma-international.org/15.0/#sec-getarraybuffermaxbytelengthoption
+
+module.exports = function GetArrayBufferMaxByteLengthOption(options) {
+	if (!isObject(options)) {
+		return 'EMPTY'; // step 1
+	}
+
+	var maxByteLength = Get(options, 'maxByteLength'); // step 2
+
+	if (typeof maxByteLength === 'undefined') {
+		return 'EMPTY'; // step 3
+	}
+
+	return ToIndex(maxByteLength); // step 4
+};