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/data-view-byte-offset/index.js

@@ -0,0 +1,19 @@
+'use strict';
+
+var $TypeError = require('es-errors/type');
+
+var callBound = require('call-bound');
+
+var $dataViewByteOffset = callBound('DataView.prototype.byteOffset', true);
+
+var isDataView = require('is-data-view');
+
+// node <= 0.10, < 0.11.4 has a nonconfigurable own property instead of a prototype getter
+/** @type {import('.')} */
+module.exports = $dataViewByteOffset || function byteOffset(x) {
+	if (!isDataView(x)) {
+		throw new $TypeError('not a DataView');
+	}
+
+	return x.byteOffset;
+};