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/minimatch/dist/esm/brace-expressions.d.ts

@@ -0,0 +1,8 @@
+export type ParseClassResult = [
+    src: string,
+    uFlag: boolean,
+    consumed: number,
+    hasMagic: boolean
+];
+export declare const parseClass: (glob: string, position: number) => ParseClassResult;
+//# sourceMappingURL=brace-expressions.d.ts.map