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/notebook-tabs.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: "M2 6h4", key: "aawbzj" }],
+  ["path", { d: "M2 10h4", key: "l0bgd4" }],
+  ["path", { d: "M2 14h4", key: "1gsvsf" }],
+  ["path", { d: "M2 18h4", key: "1bu2t1" }],
+  ["rect", { width: "16", height: "20", x: "4", y: "2", rx: "2", key: "1nb95v" }],
+  ["path", { d: "M15 2v20", key: "dcj49h" }],
+  ["path", { d: "M15 7h5", key: "1xj5lc" }],
+  ["path", { d: "M15 12h5", key: "w5shd9" }],
+  ["path", { d: "M15 17h5", key: "1qaofu" }]
+];
+const NotebookTabs = createLucideIcon("notebook-tabs", __iconNode);
+
+export { __iconNode, NotebookTabs as default };
+//# sourceMappingURL=notebook-tabs.mjs.map