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/2025/GeneratorResume.js

@@ -0,0 +1,29 @@
+'use strict';
+
+var $TypeError = require('es-errors/type');
+
+var CreateIteratorResultObject = require('./CreateIteratorResultObject');
+var GeneratorValidate = require('./GeneratorValidate');
+
+var SLOT = require('internal-slot');
+
+// https://262.ecma-international.org/16.0/#sec-generatorresume
+
+module.exports = function GeneratorResume(generator, value, generatorBrand) {
+	var state = GeneratorValidate(generator, generatorBrand); // step 1
+	if (state === 'COMPLETED') {
+		return CreateIteratorResultObject(void undefined, true); // step 2
+	}
+
+	if (state !== 'SUSPENDED-START' && state !== 'SUSPENDED-YIELD') {
+		throw new $TypeError('Assertion failed: generator state is unexpected: ' + state); // step 3
+	}
+
+	var genContext = SLOT.get(generator, '[[GeneratorContext]]');
+
+	SLOT.set(generator, '[[GeneratorState]]', 'EXECUTING'); // step 7
+
+	var result = genContext(value); // steps 5-6, 8-10
+
+	return result;
+};