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/battery-plus.mjs

@@ -0,0 +1,20 @@
+/**
+ * @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: "M10 9v6", key: "17i7lo" }],
+  ["path", { d: "M12.543 6H16a2 2 0 0 1 2 2v8a2 2 0 0 1-2 2h-3.605", key: "o09yah" }],
+  ["path", { d: "M22 14v-4", key: "14q9d5" }],
+  ["path", { d: "M7 12h6", key: "iekk3h" }],
+  ["path", { d: "M7.606 18H4a2 2 0 0 1-2-2V8a2 2 0 0 1 2-2h3.606", key: "xyqvf1" }]
+];
+const BatteryPlus = createLucideIcon("battery-plus", __iconNode);
+
+export { __iconNode, BatteryPlus as default };
+//# sourceMappingURL=battery-plus.mjs.map