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/tests.js

@@ -0,0 +1,36 @@
+/* jscs:disable requireUseStrict */
+/* eslint strict: 0, max-statements: 0 */
+
+module.exports = function (theGlobal, t) {
+	t.equal(typeof theGlobal, 'object', 'is an object');
+
+	t.test('built-in globals', function (st) {
+		st.equal(theGlobal.Math, Math, 'Math is on the global');
+		st.equal(theGlobal.JSON, JSON, 'JSON is on the global');
+		st.equal(theGlobal.String, String, 'String is on the global');
+		st.equal(theGlobal.Array, Array, 'Array is on the global');
+		st.equal(theGlobal.Number, Number, 'Number is on the global');
+		st.equal(theGlobal.Boolean, Boolean, 'Boolean is on the global');
+		st.equal(theGlobal.Object, Object, 'Object is on the global');
+		st.equal(theGlobal.Function, Function, 'Function is on the global');
+		st.equal(theGlobal.Date, Date, 'Date is on the global');
+		st.equal(theGlobal.RegExp, RegExp, 'RegExp is on the global');
+
+		if (typeof Symbol === 'undefined') {
+			st.comment('# SKIP Symbol is not supported');
+		} else {
+			st.equal(theGlobal.Symbol, Symbol, 'Symbol is on the global');
+		}
+		st.end();
+	});
+
+	t.test('custom property', function (st) {
+		var key = 'random_custom_key_' + new Date().getTime();
+		var semaphore = {};
+		/* eslint no-eval: 1 */
+		eval(key + ' = semaphore;');
+		st.equal(theGlobal[key], semaphore, 'global variable ends up on the global object');
+		delete theGlobal[key]; // eslint-disable-line no-param-reassign
+		st.end();
+	});
+};