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/object-inspect/test/fakes.js

@@ -0,0 +1,29 @@
+'use strict';
+
+var inspect = require('../');
+var test = require('tape');
+var hasToStringTag = require('has-tostringtag/shams')();
+var forEach = require('for-each');
+
+test('fakes', { skip: !hasToStringTag }, function (t) {
+    forEach([
+        'Array',
+        'Boolean',
+        'Date',
+        'Error',
+        'Number',
+        'RegExp',
+        'String'
+    ], function (expected) {
+        var faker = {};
+        faker[Symbol.toStringTag] = expected;
+
+        t.equal(
+            inspect(faker),
+            '{ [Symbol(Symbol.toStringTag)]: \'' + expected + '\' }',
+            'faker masquerading as ' + expected + ' is not shown as one'
+        );
+    });
+
+    t.end();
+});