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/sun-moon.mjs

@@ -0,0 +1,26 @@
+/**
+ * @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: "M14.837 16.385a6 6 0 1 1-7.223-7.222c.624-.147.97.66.715 1.248a4 4 0 0 0 5.26 5.259c.589-.255 1.396.09 1.248.715",
+      key: "xlf6rm"
+    }
+  ],
+  ["path", { d: "M16 12a4 4 0 0 0-4-4", key: "6vsxu" }],
+  ["path", { d: "m19 5-1.256 1.256", key: "1yg6a6" }],
+  ["path", { d: "M20 12h2", key: "1q8mjw" }]
+];
+const SunMoon = createLucideIcon("sun-moon", __iconNode);
+
+export { __iconNode, SunMoon as default };
+//# sourceMappingURL=sun-moon.mjs.map