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/call-bind-apply-helpers/actualApply.js

@@ -0,0 +1,10 @@
+'use strict';
+
+var bind = require('function-bind');
+
+var $apply = require('./functionApply');
+var $call = require('./functionCall');
+var $reflectApply = require('./reflectApply');
+
+/** @type {import('./actualApply')} */
+module.exports = $reflectApply || bind.call($call, $apply);