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/regjsparser/README.md

@@ -0,0 +1,47 @@
+# RegJSParser
+
+Parsing the JavaScript's RegExp in JavaScript.
+
+## Installation
+
+```bash
+npm install regjsparser
+```
+
+## Usage
+
+```js
+var parse = require('regjsparser').parse;
+
+var parseTree = parse('^a'); // /^a/
+console.log(parseTree);
+
+// Toggle on/off additional features:
+var parseTree = parse('^a', '', {
+  // SEE: https://github.com/jviereck/regjsparser/pull/78
+  unicodePropertyEscape: true,
+
+  // SEE: https://github.com/jviereck/regjsparser/pull/83
+  namedGroups: true,
+
+  // SEE: https://github.com/jviereck/regjsparser/pull/89
+  lookbehind: true
+});
+console.log(parseTree);
+```
+
+## Testing
+
+To run the tests, run the following command:
+
+```bash
+npm test
+```
+
+To create a new reference file, execute…
+
+```bash
+node test/update-fixtures.js
+```
+
+…from the repo top directory.