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/shebang-command/readme.md

@@ -0,0 +1,34 @@
+# shebang-command [![Build Status](https://travis-ci.org/kevva/shebang-command.svg?branch=master)](https://travis-ci.org/kevva/shebang-command)
+
+> Get the command from a shebang
+
+
+## Install
+
+```
+$ npm install shebang-command
+```
+
+
+## Usage
+
+```js
+const shebangCommand = require('shebang-command');
+
+shebangCommand('#!/usr/bin/env node');
+//=> 'node'
+
+shebangCommand('#!/bin/bash');
+//=> 'bash'
+```
+
+
+## API
+
+### shebangCommand(string)
+
+#### string
+
+Type: `string`
+
+String containing a shebang.