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/file-stack.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: "M11 21a1 1 0 0 1-1 1H4a1 1 0 0 1-1-1v-8a1 1 0 0 1 1-1", key: "likhh7" }],
+  ["path", { d: "M16 16a1 1 0 0 1-1 1H9a1 1 0 0 1-1-1V8a1 1 0 0 1 1-1", key: "17ky3x" }],
+  [
+    "path",
+    {
+      d: "M21 6a2 2 0 0 0-.586-1.414l-2-2A2 2 0 0 0 17 2h-3a1 1 0 0 0-1 1v8a1 1 0 0 0 1 1h6a1 1 0 0 0 1-1z",
+      key: "1hyeo0"
+    }
+  ]
+];
+const FileStack = createLucideIcon("file-stack", __iconNode);
+
+export { __iconNode, FileStack as default };
+//# sourceMappingURL=file-stack.mjs.map