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/es-abstract/2015/GetMethod.js

@@ -0,0 +1,34 @@
+'use strict';
+
+var $TypeError = require('es-errors/type');
+
+var GetV = require('./GetV');
+var IsCallable = require('./IsCallable');
+var isPropertyKey = require('../helpers/isPropertyKey');
+
+var inspect = require('object-inspect');
+
+// https://262.ecma-international.org/6.0/#sec-getmethod
+
+module.exports = function GetMethod(O, P) {
+	// 7.3.9.1
+	if (!isPropertyKey(P)) {
+		throw new $TypeError('Assertion failed: P is not a Property Key');
+	}
+
+	// 7.3.9.2
+	var func = GetV(O, P);
+
+	// 7.3.9.4
+	if (func == null) {
+		return void 0;
+	}
+
+	// 7.3.9.5
+	if (!IsCallable(func)) {
+		throw new $TypeError(inspect(P) + ' is not a function: ' + inspect(func));
+	}
+
+	// 7.3.9.6
+	return func;
+};