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/is-core-module/README.md

@@ -0,0 +1,40 @@
+# is-core-module <sup>[![Version Badge][2]][1]</sup>
+
+[![github actions][actions-image]][actions-url]
+[![coverage][codecov-image]][codecov-url]
+[![dependency status][5]][6]
+[![dev dependency status][7]][8]
+[![License][license-image]][license-url]
+[![Downloads][downloads-image]][downloads-url]
+
+[![npm badge][11]][1]
+
+Is this specifier a node.js core module? Optionally provide a node version to check; defaults to the current node version.
+
+## Example
+
+```js
+var isCore = require('is-core-module');
+var assert = require('assert');
+assert(isCore('fs'));
+assert(!isCore('butts'));
+```
+
+## Tests
+Clone the repo, `npm install`, and run `npm test`
+
+[1]: https://npmjs.org/package/is-core-module
+[2]: https://versionbadg.es/inspect-js/is-core-module.svg
+[5]: https://david-dm.org/inspect-js/is-core-module.svg
+[6]: https://david-dm.org/inspect-js/is-core-module
+[7]: https://david-dm.org/inspect-js/is-core-module/dev-status.svg
+[8]: https://david-dm.org/inspect-js/is-core-module#info=devDependencies
+[11]: https://nodei.co/npm/is-core-module.png?downloads=true&stars=true
+[license-image]: https://img.shields.io/npm/l/is-core-module.svg
+[license-url]: LICENSE
+[downloads-image]: https://img.shields.io/npm/dm/is-core-module.svg
+[downloads-url]: https://npm-stat.com/charts.html?package=is-core-module
+[codecov-image]: https://codecov.io/gh/inspect-js/is-core-module/branch/main/graphs/badge.svg
+[codecov-url]: https://app.codecov.io/gh/inspect-js/is-core-module/
+[actions-image]: https://img.shields.io/github/check-runs/inspect-js/is-core-module/main
+[actions-url]: https://github.com/inspect-js/is-core-module/actions