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/call-bind-apply-helpers/applyBind.d.ts

@@ -0,0 +1,19 @@
+import actualApply from './actualApply';
+
+type TupleSplitHead<T extends any[], N extends number> = T['length'] extends N
+  ? T
+  : T extends [...infer R, any]
+  ? TupleSplitHead<R, N>
+  : never
+
+type TupleSplitTail<T, N extends number, O extends any[] = []> = O['length'] extends N
+  ? T
+  : T extends [infer F, ...infer R]
+  ? TupleSplitTail<[...R], N, [...O, F]>
+  : never
+
+type TupleSplit<T extends any[], N extends number> = [TupleSplitHead<T, N>, TupleSplitTail<T, N>]
+
+declare function applyBind(...args: TupleSplit<Parameters<typeof actualApply>, 2>[1]): ReturnType<typeof actualApply>;
+
+export = applyBind;