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/globalthis/test/shimmed.js

@@ -0,0 +1,29 @@
+'use strict';
+
+require('../auto');
+
+var test = require('tape');
+var defineProperties = require('define-properties');
+var isEnumerable = Object.prototype.propertyIsEnumerable;
+
+var runTests = require('./tests');
+
+test('shimmed', function (t) {
+	t.equal(typeof globalThis, 'object', 'globalThis is an object');
+	t.equal('globalThis' in globalThis, true, 'globalThis is in globalThis');
+
+	t.test('enumerability', { skip: !defineProperties.supportsDescriptors }, function (et) {
+		et.equal(false, isEnumerable.call(globalThis, 'globalThis'), 'globalThis.globalThis is not enumerable');
+		et.end();
+	});
+
+	t.test('writability', { skip: !defineProperties.supportsDescriptors }, function (wt) {
+		var desc = Object.getOwnPropertyDescriptor(globalThis, 'globalThis');
+		wt.equal(desc.writable, true, 'globalThis.globalThis is writable');
+		wt.end();
+	});
+
+	runTests(globalThis.globalThis, t);
+
+	t.end();
+});