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/move-diagonal-2.mjs

@@ -0,0 +1,18 @@
+/**
+ * @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: "M19 13v6h-6", key: "1hxl6d" }],
+  ["path", { d: "M5 11V5h6", key: "12e2xe" }],
+  ["path", { d: "m5 5 14 14", key: "11anup" }]
+];
+const MoveDiagonal2 = createLucideIcon("move-diagonal-2", __iconNode);
+
+export { __iconNode, MoveDiagonal2 as default };
+//# sourceMappingURL=move-diagonal-2.mjs.map