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-charging.mjs

@@ -0,0 +1,19 @@
+/**
+ * @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: "m11 7-3 5h4l-3 5", key: "b4a64w" }],
+  ["path", { d: "M14.856 6H16a2 2 0 0 1 2 2v8a2 2 0 0 1-2 2h-2.935", key: "lre1cr" }],
+  ["path", { d: "M22 14v-4", key: "14q9d5" }],
+  ["path", { d: "M5.14 18H4a2 2 0 0 1-2-2V8a2 2 0 0 1 2-2h2.936", key: "13q5k0" }]
+];
+const BatteryCharging = createLucideIcon("battery-charging", __iconNode);
+
+export { __iconNode, BatteryCharging as default };
+//# sourceMappingURL=battery-charging.mjs.map