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/squares-unite.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: "M4 16a2 2 0 0 1-2-2V4a2 2 0 0 1 2-2h10a2 2 0 0 1 2 2v3a1 1 0 0 0 1 1h3a2 2 0 0 1 2 2v10a2 2 0 0 1-2 2H10a2 2 0 0 1-2-2v-3a1 1 0 0 0-1-1z",
+      key: "17jnth"
+    }
+  ]
+];
+const SquaresUnite = createLucideIcon("squares-unite", __iconNode);
+
+export { __iconNode, SquaresUnite as default };
+//# sourceMappingURL=squares-unite.mjs.map