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/calendar-x.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: "M8 2v4", key: "1cmpym" }],
+  ["path", { d: "M16 2v4", key: "4m81vk" }],
+  ["rect", { width: "18", height: "18", x: "3", y: "4", rx: "2", key: "1hopcy" }],
+  ["path", { d: "M3 10h18", key: "8toen8" }],
+  ["path", { d: "m14 14-4 4", key: "rymu2i" }],
+  ["path", { d: "m10 14 4 4", key: "3sz06r" }]
+];
+const CalendarX = createLucideIcon("calendar-x", __iconNode);
+
+export { __iconNode, CalendarX as default };
+//# sourceMappingURL=calendar-x.mjs.map