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/temp-dir/readme.md

@@ -0,0 +1,30 @@
+# temp-dir [![Build Status](https://travis-ci.org/sindresorhus/temp-dir.svg?branch=master)](https://travis-ci.org/sindresorhus/temp-dir)
+
+> Get the real path of the system temp directory
+
+[The `os.tmpdir()` built-in doesn't return the real path.](https://github.com/nodejs/node/issues/11422) That can cause problems when the returned path is a symlink, which is the case on macOS. Use this module to get the resolved path.
+
+
+## Install
+
+```
+$ npm install temp-dir
+```
+
+
+## Usage
+
+```js
+const tempDirectory = require('temp-dir');
+
+console.log(tempDirectory);
+//=> '/private/var/folders/3x/jf5977fn79jbglr7rk0tq4d00000gn/T'
+
+console.log(require('os').tmpdir());
+//=> '/var/folders/3x/jf5977fn79jbglr7rk0tq4d00000gn/T' // <= Symlink
+```
+
+
+## License
+
+MIT © [Sindre Sorhus](https://sindresorhus.com)