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/@babel/plugin-proposal-private-property-in-object/README.md

@@ -0,0 +1,23 @@
+# @babel/plugin-proposal-private-property-in-object
+
+> ⚠️ This version of the package (`v7.21.0-placeholder-for-preset-env.1`) is not meant to
+> be imported. Use any other version of this plugin or, even better, the
+> [@babel/plugin-transform-private-property-in-object](https://babeljs.io/docs/en/babel-plugin-transform-private-property-in-object) package.
+
+> This plugin transforms checks for a private property in an object
+
+See our website [@babel/plugin-proposal-private-property-in-object](https://babeljs.io/docs/en/babel-plugin-proposal-private-property-in-object) for more information.
+
+## Install
+
+Using npm:
+
+```sh
+npm install --save-dev @babel/plugin-proposal-private-property-in-object
+```
+
+or using yarn:
+
+```sh
+yarn add @babel/plugin-proposal-private-property-in-object --dev
+```