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/leven/readme.md

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+# leven [![Build Status](https://travis-ci.org/sindresorhus/leven.svg?branch=master)](https://travis-ci.org/sindresorhus/leven)
+
+> Measure the difference between two strings<br>
+> One of the fastest JS implementations of the [Levenshtein distance](https://en.wikipedia.org/wiki/Levenshtein_distance) algorithm
+
+
+## Install
+
+```
+$ npm install leven
+```
+
+
+## Usage
+
+```js
+const leven = require('leven');
+
+leven('cat', 'cow');
+//=> 2
+```
+
+
+## Benchmark
+
+```
+$ npm run bench
+```
+
+```
+         165,926 op/s » leven
+         164,398 op/s » talisman
+           1,044 op/s » levenshtein-edit-distance
+             628 op/s » fast-levenshtein
+             497 op/s » levenshtein-component
+             195 op/s » ld
+             190 op/s » levenshtein
+             168 op/s » levdist
+              10 op/s » natural
+```
+
+
+## Related
+
+- [leven-cli](https://github.com/sindresorhus/leven-cli) - CLI for this module
+
+
+## License
+
+MIT © [Sindre Sorhus](https://sindresorhus.com)