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/lucide-react/dist/esm/icons/book-copy.mjs

@@ -0,0 +1,24 @@
+/**
+ * @license lucide-react v1.24.0 - ISC
+ *
+ * This source code is licensed under the ISC license.
+ * See the LICENSE file in the root directory of this source tree.
+ */
+
+import createLucideIcon from '../createLucideIcon.mjs';
+
+const __iconNode = [
+  ["path", { d: "M5 7a2 2 0 0 0-2 2v11", key: "1yhqjt" }],
+  ["path", { d: "M5.803 18H5a2 2 0 0 0 0 4h9.5a.5.5 0 0 0 .5-.5V21", key: "edzzo5" }],
+  [
+    "path",
+    {
+      d: "M9 15V4a2 2 0 0 1 2-2h9.5a.5.5 0 0 1 .5.5v14a.5.5 0 0 1-.5.5H11a2 2 0 0 1 0-4h10",
+      key: "1nwzrg"
+    }
+  ]
+];
+const BookCopy = createLucideIcon("book-copy", __iconNode);
+
+export { __iconNode, BookCopy as default };
+//# sourceMappingURL=book-copy.mjs.map