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-to-primitive/test/index.js

@@ -0,0 +1,20 @@
+'use strict';
+
+var toPrimitive = require('../');
+var ES5 = require('../es5');
+var ES6 = require('../es6');
+var ES2015 = require('../es2015');
+
+var test = require('tape');
+
+test('default export', function (t) {
+	t.equal(toPrimitive, ES2015, 'default export is ES2015');
+	t.equal(toPrimitive.ES5, ES5, 'ES5 property has ES5 method');
+	t.equal(toPrimitive.ES6, ES6, 'ES6 property has ES6 method');
+	t.equal(toPrimitive.ES2015, ES2015, 'ES2015 property has ES2015 method');
+	t.end();
+});
+
+require('./es5');
+require('./es6');
+require('./es2015');