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/utils/getCacheKeyForURL.js

@@ -0,0 +1,31 @@
+/*
+  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 './getOrCreatePrecacheController.js';
+import { generateURLVariations } from './generateURLVariations.js';
+import '../_version.js';
+/**
+ * This function will take the request URL and manipulate it based on the
+ * configuration options.
+ *
+ * @param {string} url
+ * @param {Object} options
+ * @return {string} Returns the URL in the cache that matches the request,
+ * if possible.
+ *
+ * @private
+ */
+export const getCacheKeyForURL = (url, options) => {
+    const precacheController = getOrCreatePrecacheController();
+    const urlsToCacheKeys = precacheController.getURLsToCacheKeys();
+    for (const possibleURL of generateURLVariations(url, options)) {
+        const possibleCacheKey = urlsToCacheKeys.get(possibleURL);
+        if (possibleCacheKey) {
+            return possibleCacheKey;
+        }
+    }
+};