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/jake/lib/task/index.js

@@ -0,0 +1,9 @@
+
+let Task = require('./task').Task;
+let FileTask = require('./file_task').FileTask;
+let DirectoryTask = require('./directory_task').DirectoryTask;
+
+exports.Task = Task;
+exports.FileTask = FileTask;
+exports.DirectoryTask = DirectoryTask;
+