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/calendars.mjs

@@ -0,0 +1,21 @@
+/**
+ * @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: "M12 2v2", key: "tus03m" }],
+  ["path", { d: "M15.726 21.01A2 2 0 0 1 14 22H4a2 2 0 0 1-2-2V10a2 2 0 0 1 2-2", key: "j6srht" }],
+  ["path", { d: "M18 2v2", key: "1kh14s" }],
+  ["path", { d: "M2 13h2", key: "13gyu8" }],
+  ["path", { d: "M8 8h14", key: "12jxz2" }],
+  ["rect", { x: "8", y: "3", width: "14", height: "14", rx: "2", key: "nsru6w" }]
+];
+const Calendars = createLucideIcon("calendars", __iconNode);
+
+export { __iconNode, Calendars as default };
+//# sourceMappingURL=calendars.mjs.map