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/GetViewByteLength.js

@@ -0,0 +1,47 @@
+'use strict';
+
+var $TypeError = require('es-errors/type');
+
+var IsFixedLengthArrayBuffer = require('./IsFixedLengthArrayBuffer');
+var IsViewOutOfBounds = require('./IsViewOutOfBounds');
+
+var isDataViewWithBufferWitnessRecord = require('../helpers/records/data-view-with-buffer-witness-record');
+
+var dataViewBuffer = require('data-view-buffer');
+var dataViewByteLength = require('data-view-byte-length');
+var dataViewByteOffset = require('data-view-byte-offset');
+
+// https://262.ecma-international.org/15.0/#sec-getviewbytelength
+
+module.exports = function GetViewByteLength(viewRecord) {
+	if (!isDataViewWithBufferWitnessRecord(viewRecord)) {
+		throw new $TypeError('Assertion failed: `viewRecord` must be a DataView with Buffer Witness Record');
+	}
+
+	if (IsViewOutOfBounds(viewRecord)) {
+		throw new $TypeError('Assertion failed: `viewRecord` is out of bounds'); // step 1
+	}
+
+	var view = viewRecord['[[Object]]']; // step 2
+
+	var isFixed = IsFixedLengthArrayBuffer(dataViewBuffer(view));
+
+	var viewByteLength = isFixed ? dataViewByteLength(view) : 'AUTO'; // view.[[ByteLength]]
+	if (viewByteLength !== 'AUTO') {
+		return viewByteLength; // step 3
+	}
+
+	if (isFixed) {
+		throw new $TypeError('Assertion failed: DataView’s ArrayBuffer is not fixed length'); // step 4
+	}
+
+	var byteOffset = dataViewByteOffset(view); // step 5
+
+	var byteLength = viewRecord['[[CachedBufferByteLength]]']; // step 6
+
+	if (byteLength === 'DETACHED') {
+		throw new $TypeError('Assertion failed: DataView’s ArrayBuffer is detached'); // step 7
+	}
+
+	return byteLength - byteOffset; // step 8
+};