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/flip-horizontal-2.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: "m3 7 5 5-5 5V7", key: "couhi7" }],
+  ["path", { d: "m21 7-5 5 5 5V7", key: "6ouia7" }],
+  ["path", { d: "M12 20v2", key: "1lh1kg" }],
+  ["path", { d: "M12 14v2", key: "8jcxud" }],
+  ["path", { d: "M12 8v2", key: "1woqiv" }],
+  ["path", { d: "M12 2v2", key: "tus03m" }]
+];
+const FlipHorizontal2 = createLucideIcon("flip-horizontal-2", __iconNode);
+
+export { __iconNode, FlipHorizontal2 as default };
+//# sourceMappingURL=flip-horizontal-2.mjs.map