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/arrow-big-up.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: "M9 19a1 1 0 0 0 1 1h4a1 1 0 0 0 1-1v-6a1 1 0 0 1 1-1h3.293a.707.707 0 0 0 .5-1.207l-7.086-7.086a1 1 0 0 0-1.414 0l-7.086 7.086a.707.707 0 0 0 .5 1.207H8a1 1 0 0 1 1 1z",
+      key: "106j91"
+    }
+  ]
+];
+const ArrowBigUp = createLucideIcon("arrow-big-up", __iconNode);
+
+export { __iconNode, ArrowBigUp as default };
+//# sourceMappingURL=arrow-big-up.mjs.map