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-stack.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: "M4 10c-1.1 0-2-.9-2-2V4c0-1.1.9-2 2-2h4c1.1 0 2 .9 2 2", key: "4i38lg" }],
+  ["path", { d: "M10 16c-1.1 0-2-.9-2-2v-4c0-1.1.9-2 2-2h4c1.1 0 2 .9 2 2", key: "mlte4a" }],
+  ["rect", { width: "8", height: "8", x: "14", y: "14", rx: "2", key: "1fa9i4" }]
+];
+const SquareStack = createLucideIcon("square-stack", __iconNode);
+
+export { __iconNode, SquareStack as default };
+//# sourceMappingURL=square-stack.mjs.map