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/IsArrayBufferViewOutOfBounds.js

@@ -0,0 +1,30 @@
+'use strict';
+
+var $TypeError = require('es-errors/type');
+
+var IsTypedArrayOutOfBounds = require('./IsTypedArrayOutOfBounds');
+var IsViewOutOfBounds = require('./IsViewOutOfBounds');
+var MakeDataViewWithBufferWitnessRecord = require('./MakeDataViewWithBufferWitnessRecord');
+var MakeTypedArrayWithBufferWitnessRecord = require('./MakeTypedArrayWithBufferWitnessRecord');
+
+var isDataView = require('is-data-view');
+var isTypedArray = require('is-typed-array');
+
+// https://262.ecma-international.org/15.0/#sec-isarraybufferviewoutofbounds
+
+module.exports = function IsArrayBufferViewOutOfBounds(O) {
+	var isDV = isDataView(O);
+	if (!isTypedArray(O) && !isDV) {
+		throw new $TypeError('Assertion failed: `O` must be a TypedArray or DataView');
+	}
+
+	if (isDV) { // step 1
+		var viewRecord = MakeDataViewWithBufferWitnessRecord(O, 'SEQ-CST'); // step 1.a
+
+		return IsViewOutOfBounds(viewRecord); // step 1.b
+	}
+
+	var taRecord = MakeTypedArrayWithBufferWitnessRecord(O, 'SEQ-CST'); // step 2
+
+	return IsTypedArrayOutOfBounds(taRecord); // step 3
+};