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/sigma.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: "M18 7V5a1 1 0 0 0-1-1H6.5a.5.5 0 0 0-.4.8l4.5 6a2 2 0 0 1 0 2.4l-4.5 6a.5.5 0 0 0 .4.8H17a1 1 0 0 0 1-1v-2",
+      key: "wuwx1p"
+    }
+  ]
+];
+const Sigma = createLucideIcon("sigma", __iconNode);
+
+export { __iconNode, Sigma as default };
+//# sourceMappingURL=sigma.mjs.map