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/sliders-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: "M10 8h4", key: "1sr2af" }],
+  ["path", { d: "M12 21v-9", key: "17s77i" }],
+  ["path", { d: "M12 8V3", key: "13r4qs" }],
+  ["path", { d: "M17 16h4", key: "h1uq16" }],
+  ["path", { d: "M19 12V3", key: "o1uvq1" }],
+  ["path", { d: "M19 21v-5", key: "qua636" }],
+  ["path", { d: "M3 14h4", key: "bcjad9" }],
+  ["path", { d: "M5 10V3", key: "cb8scm" }],
+  ["path", { d: "M5 21v-7", key: "1w1uti" }]
+];
+const SlidersVertical = createLucideIcon("sliders-vertical", __iconNode);
+
+export { __iconNode, SlidersVertical as default };
+//# sourceMappingURL=sliders-vertical.mjs.map