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/async-function/test/index.js

@@ -0,0 +1,40 @@
+'use strict';
+
+var test = require('tape');
+var getProto = require('get-proto');
+var semver = require('semver');
+
+var getAsyncFunction = require('../');
+
+test('getAsyncFunction', function (t) {
+	var result = getAsyncFunction();
+
+	/* eslint-env browser */
+	if (typeof window === 'undefined' && typeof process !== 'undefined') {
+		t.equal(
+			!!result,
+			semver.satisfies(process.version, '>= 7.6'),
+			'result is present or absent as expected for node ' + process.version
+		);
+	}
+
+	t.test('exists', { skip: !result }, function (st) {
+		if (result && getProto) { // TS can't infer `skip`, or that getProto definitely exists if AsyncFunction exists
+			st.equal(typeof result, 'function', 'is a function');
+			st.equal(getProto(result), Function, 'extends Function');
+
+			return result('a', 'return a')(42).then(function (a) {
+				st.equal(a, 42, 'returns an async function');
+			});
+		}
+		return st.fail('should never get here');
+	});
+
+	t.test('does not exist', { skip: !!result }, function (st) {
+		st.equal(result, false, 'is false');
+
+		st.end();
+	});
+
+	t.end();
+});