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/supports-preserve-symlinks-flag/test/index.js

@@ -0,0 +1,29 @@
+'use strict';
+
+var test = require('tape');
+var semver = require('semver');
+
+var supportsPreserveSymlinks = require('../');
+var browser = require('../browser');
+
+test('supportsPreserveSymlinks', function (t) {
+	t.equal(typeof supportsPreserveSymlinks, 'boolean', 'is a boolean');
+
+	t.equal(browser, null, 'browser file is `null`');
+	t.equal(
+		supportsPreserveSymlinks,
+		null,
+		'in a browser, is null',
+		{ skip: typeof window === 'undefined' }
+	);
+
+	var expected = semver.satisfies(process.version, '>= 6.2');
+	t.equal(
+		supportsPreserveSymlinks,
+		expected,
+		'is true in node v6.2+, false otherwise (actual: ' + supportsPreserveSymlinks + ', expected ' + expected + ')',
+		{ skip: typeof window !== 'undefined' }
+	);
+
+	t.end();
+});