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/index.js

@@ -0,0 +1,19 @@
+'use strict';
+const shebangRegex = require('shebang-regex');
+
+module.exports = (string = '') => {
+	const match = string.match(shebangRegex);
+
+	if (!match) {
+		return null;
+	}
+
+	const [path, argument] = match[0].replace(/#! ?/, '').split(' ');
+	const binary = path.split('/').pop();
+
+	if (binary === 'env') {
+		return argument;
+	}
+
+	return argument ? `${binary} ${argument}` : binary;
+};