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/global.js

@@ -0,0 +1,17 @@
+'use strict';
+
+var inspect = require('../');
+
+var test = require('tape');
+var globalThis = require('globalthis')();
+
+test('global object', function (t) {
+    /* eslint-env browser */
+    var expected = typeof window === 'undefined' ? 'globalThis' : 'Window';
+    t.equal(
+        inspect([globalThis]),
+        '[ { [object ' + expected + '] } ]'
+    );
+
+    t.end();
+});