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/2025/MakeDataViewWithBufferWitnessRecord.js

@@ -0,0 +1,26 @@
+'use strict';
+
+var $TypeError = require('es-errors/type');
+
+var ArrayBufferByteLength = require('./ArrayBufferByteLength');
+var IsDetachedBuffer = require('./IsDetachedBuffer');
+
+var dataViewBuffer = require('data-view-buffer');
+var isDataView = require('is-data-view');
+
+// https://262.ecma-international.org/15.0/#sec-makedataviewwithbufferwitnessrecord
+
+module.exports = function MakeDataViewWithBufferWitnessRecord(obj, order) {
+	if (!isDataView(obj)) {
+		throw new $TypeError('MakeDataViewWithBufferWitnessRecord called with non-DataView');
+	}
+	if (order !== 'SEQ-CST' && order !== 'UNORDERED') {
+		throw new $TypeError('Assertion failed: `order` must be ~SEQ-CST~ or ~UNORDERED~');
+	}
+
+	var buffer = dataViewBuffer(obj); // step 1
+
+	var byteLength = IsDetachedBuffer(buffer) ? 'DETACHED' : ArrayBufferByteLength(buffer, order); // steps 2 - 3
+
+	return { '[[Object]]': obj, '[[CachedBufferByteLength]]': byteLength }; // step 4
+};