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-centerline-dashed-vertical.mjs

@@ -0,0 +1,24 @@
+/**
+ * @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 8V5a2 2 0 0 0-2-2H5a2 2 0 0 0-2 2v3", key: "14bfxa" }],
+  ["path", { d: "M21 16v3a2 2 0 0 1-2 2H5a2 2 0 0 1-2-2v-3", key: "14rx03" }],
+  ["path", { d: "M4 12H2", key: "rhcxmi" }],
+  ["path", { d: "M10 12H8", key: "s88cx1" }],
+  ["path", { d: "M16 12h-2", key: "10asgb" }],
+  ["path", { d: "M22 12h-2", key: "14jgyd" }]
+];
+const SquareCenterlineDashedVertical = createLucideIcon(
+  "square-centerline-dashed-vertical",
+  __iconNode
+);
+
+export { __iconNode, SquareCenterlineDashedVertical as default };
+//# sourceMappingURL=square-centerline-dashed-vertical.mjs.map