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-arrow-out-down-right.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: "M21 11V5a2 2 0 0 0-2-2H5a2 2 0 0 0-2 2v14a2 2 0 0 0 2 2h6", key: "14rsvq" }],
+  ["path", { d: "m21 21-9-9", key: "1et2py" }],
+  ["path", { d: "M21 15v6h-6", key: "1jko0i" }]
+];
+const SquareArrowOutDownRight = createLucideIcon("square-arrow-out-down-right", __iconNode);
+
+export { __iconNode, SquareArrowOutDownRight as default };
+//# sourceMappingURL=square-arrow-out-down-right.mjs.map