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/has-symbols/test/index.js

@@ -0,0 +1,22 @@
+'use strict';
+
+var test = require('tape');
+var hasSymbols = require('../');
+var runSymbolTests = require('./tests');
+
+test('interface', function (t) {
+	t.equal(typeof hasSymbols, 'function', 'is a function');
+	t.equal(typeof hasSymbols(), 'boolean', 'returns a boolean');
+	t.end();
+});
+
+test('Symbols are supported', { skip: !hasSymbols() }, function (t) {
+	runSymbolTests(t);
+	t.end();
+});
+
+test('Symbols are not supported', { skip: hasSymbols() }, function (t) {
+	t.equal(typeof Symbol, 'undefined', 'global Symbol is undefined');
+	t.equal(typeof Object.getOwnPropertySymbols, 'undefined', 'Object.getOwnPropertySymbols does not exist');
+	t.end();
+});