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/jake/README.md

@@ -0,0 +1,17 @@
+### Jake -- the JavaScript build tool for Node.js
+
+[![Build Status](https://travis-ci.org/jakejs/jake.svg?branch=master)](https://travis-ci.org/jakejs/jake)
+
+Documentation site at [http://jakejs.com](http://jakejs.com/)
+
+### Contributing
+1. [Install node](http://nodejs.org/#download).
+2. Clone this repository `$ git clone git@github.com:jakejs/jake.git`.
+3. Install dependencies `$ npm install`.
+4. Run tests with `$ npm test`.
+5. Start Hacking!
+
+### License
+
+Licensed under the Apache License, Version 2.0
+(<http://www.apache.org/licenses/LICENSE-2.0>)