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/filelist/jakefile.js

@@ -0,0 +1,15 @@
+testTask('FileList', function () {
+  this.testFiles.include('test/*.js');
+});
+
+publishTask('FileList', function () {
+  this.packageFiles.include([
+  'jakefile.js',
+  'README.md',
+  'package.json',
+  'index.js',
+  'index.d.ts'
+  ]);
+});
+
+