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/dice-6.mjs

@@ -0,0 +1,22 @@
+/**
+ * @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 = [
+  ["rect", { width: "18", height: "18", x: "3", y: "3", rx: "2", ry: "2", key: "1m3agn" }],
+  ["path", { d: "M16 8h.01", key: "cr5u4v" }],
+  ["path", { d: "M16 12h.01", key: "1l6xoz" }],
+  ["path", { d: "M16 16h.01", key: "1f9h7w" }],
+  ["path", { d: "M8 8h.01", key: "1e4136" }],
+  ["path", { d: "M8 12h.01", key: "czm47f" }],
+  ["path", { d: "M8 16h.01", key: "18s6g9" }]
+];
+const Dice6 = createLucideIcon("dice-6", __iconNode);
+
+export { __iconNode, Dice6 as default };
+//# sourceMappingURL=dice-6.mjs.map