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/cassette-tape.mjs

@@ -0,0 +1,20 @@
+/**
+ * @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: "20", height: "16", x: "2", y: "4", rx: "2", key: "18n3k1" }],
+  ["circle", { cx: "8", cy: "10", r: "2", key: "1xl4ub" }],
+  ["path", { d: "M8 12h8", key: "1wcyev" }],
+  ["circle", { cx: "16", cy: "10", r: "2", key: "r14t7q" }],
+  ["path", { d: "m6 20 .7-2.9A1.4 1.4 0 0 1 8.1 16h7.8a1.4 1.4 0 0 1 1.4 1l.7 3", key: "l01ucn" }]
+];
+const CassetteTape = createLucideIcon("cassette-tape", __iconNode);
+
+export { __iconNode, CassetteTape as default };
+//# sourceMappingURL=cassette-tape.mjs.map