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-regexp/index.js

@@ -0,0 +1,4 @@
+'use strict';
+module.exports = function (re) {
+	return Object.prototype.toString.call(re) === '[object RegExp]';
+};

frontend/node_modules/is-regexp/package.json

@@ -0,0 +1,35 @@
+{
+  "name": "is-regexp",
+  "version": "1.0.0",
+  "description": "Check whether a variable is a regular expression",
+  "license": "MIT",
+  "repository": "sindresorhus/is-regexp",
+  "author": {
+    "name": "Sindre Sorhus",
+    "email": "sindresorhus@gmail.com",
+    "url": "http://sindresorhus.com"
+  },
+  "engines": {
+    "node": ">=0.10.0"
+  },
+  "scripts": {
+    "test": "mocha"
+  },
+  "files": [
+    "index.js"
+  ],
+  "keywords": [
+    "regex",
+    "regexp",
+    "regular",
+    "expression",
+    "regular expression",
+    "re",
+    "check",
+    "type",
+    "is"
+  ],
+  "devDependencies": {
+    "mocha": "*"
+  }
+}

frontend/node_modules/is-regexp/readme.md

@@ -0,0 +1,31 @@
+# is-regexp [![Build Status](https://travis-ci.org/sindresorhus/is-regexp.svg?branch=master)](https://travis-ci.org/sindresorhus/is-regexp)
+
+> Check whether a variable is a regular expression
+
+
+## Install
+
+```sh
+$ npm install --save is-regexp
+```
+
+
+## Usage
+
+```js
+var isRegexp = require('is-regexp');
+
+isRegexp('unicorn');
+//=> false
+
+isRegexp(/unicorn/);
+//=> true
+
+isRegexp(new RegExp('unicorn'));
+//=> true
+```
+
+
+## License
+
+MIT © [Sindre Sorhus](http://sindresorhus.com)