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/square-split-vertical.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: "M5 8V5c0-1 1-2 2-2h10c1 0 2 1 2 2v3", key: "1pi83i" }],
+  ["path", { d: "M19 16v3c0 1-1 2-2 2H7c-1 0-2-1-2-2v-3", key: "ido5k7" }],
+  ["line", { x1: "4", x2: "20", y1: "12", y2: "12", key: "1e0a9i" }]
+];
+const SquareSplitVertical = createLucideIcon("square-split-vertical", __iconNode);
+
+export { __iconNode, SquareSplitVertical as default };
+//# sourceMappingURL=square-split-vertical.mjs.map