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/helpers/fromPropertyDescriptor.js

@@ -0,0 +1,27 @@
+'use strict';
+
+module.exports = function fromPropertyDescriptor(Desc) {
+	if (typeof Desc === 'undefined') {
+		return Desc;
+	}
+	var obj = {};
+	if ('[[Value]]' in Desc) {
+		obj.value = Desc['[[Value]]'];
+	}
+	if ('[[Writable]]' in Desc) {
+		obj.writable = !!Desc['[[Writable]]'];
+	}
+	if ('[[Get]]' in Desc) {
+		obj.get = Desc['[[Get]]'];
+	}
+	if ('[[Set]]' in Desc) {
+		obj.set = Desc['[[Set]]'];
+	}
+	if ('[[Enumerable]]' in Desc) {
+		obj.enumerable = !!Desc['[[Enumerable]]'];
+	}
+	if ('[[Configurable]]' in Desc) {
+		obj.configurable = !!Desc['[[Configurable]]'];
+	}
+	return obj;
+};