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/workbox-precaching/src/matchPrecache.ts

@@ -0,0 +1,35 @@
+/*
+  Copyright 2019 Google LLC
+
+  Use of this source code is governed by an MIT-style
+  license that can be found in the LICENSE file or at
+  https://opensource.org/licenses/MIT.
+*/
+
+import {getOrCreatePrecacheController} from './utils/getOrCreatePrecacheController.js';
+
+import './_version.js';
+
+/**
+ * Helper function that calls
+ * {@link PrecacheController#matchPrecache} on the default
+ * {@link PrecacheController} instance.
+ *
+ * If you are creating your own {@link PrecacheController}, then call
+ * {@link PrecacheController#matchPrecache} on that instance,
+ * instead of using this function.
+ *
+ * @param {string|Request} request The key (without revisioning parameters)
+ * to look up in the precache.
+ * @return {Promise<Response|undefined>}
+ *
+ * @memberof workbox-precaching
+ */
+function matchPrecache(
+  request: string | Request,
+): Promise<Response | undefined> {
+  const precacheController = getOrCreatePrecacheController();
+  return precacheController.matchPrecache(request);
+}
+
+export {matchPrecache};