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/own-keys/index.js

@@ -0,0 +1,21 @@
+'use strict';
+
+var GetIntrinsic = require('get-intrinsic');
+
+var safePushApply = require('safe-push-apply');
+
+var $ownKeys = GetIntrinsic('%Reflect.ownKeys%', true);
+var $gOPN = GetIntrinsic('%Object.getOwnPropertyNames%', true);
+var $gOPS = GetIntrinsic('%Object.getOwnPropertySymbols%', true);
+
+var keys = require('object-keys');
+
+/** @type {import('.')} */
+module.exports = $ownKeys || function ownKeys(source) {
+	/** @type {(keyof typeof source)[]} */
+	var sourceKeys = ($gOPN || keys)(source);
+	if ($gOPS) {
+		safePushApply(sourceKeys, $gOPS(source));
+	}
+	return sourceKeys;
+};