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/shelving-unit.mjs

@@ -0,0 +1,22 @@
+/**
+ * @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: "M12 12V9a1 1 0 0 0-1-1H9a1 1 0 0 0-1 1v3", key: "wiz68x" }],
+  ["path", { d: "M16 20v-3a1 1 0 0 0-1-1h-2a1 1 0 0 0-1 1v3", key: "1b59c4" }],
+  ["path", { d: "M20 22V2", key: "1bnhr8" }],
+  ["path", { d: "M4 12h16", key: "1lakjw" }],
+  ["path", { d: "M4 20h16", key: "14thso" }],
+  ["path", { d: "M4 2v20", key: "gtpd5x" }],
+  ["path", { d: "M4 4h16", key: "1bkgr1" }]
+];
+const ShelvingUnit = createLucideIcon("shelving-unit", __iconNode);
+
+export { __iconNode, ShelvingUnit as default };
+//# sourceMappingURL=shelving-unit.mjs.map