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/directory_task.js

@@ -0,0 +1,30 @@
+let fs = require('fs');
+let FileTask = require('./file_task').FileTask;
+
+/**
+  @name jake
+  @namespace jake
+*/
+/**
+  @name jake.DirectoryTask
+  @constructor
+  @augments EventEmitter
+  @augments jake.Task
+  @augments jake.FileTask
+  @description A Jake DirectoryTask
+
+  @param {String} name The name of the directory to create.
+ */
+class DirectoryTask extends FileTask {
+  constructor(...args) {
+    super(...args);
+    if (fs.existsSync(this.name)) {
+      this.updateModTime();
+    }
+    else {
+      this.modTime = null;
+    }
+  }
+}
+
+exports.DirectoryTask = DirectoryTask;