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/removeIgnoredSearchParams.d.ts

@@ -0,0 +1,14 @@
+import '../_version.js';
+/**
+ * Removes any URL search parameters that should be ignored.
+ *
+ * @param {URL} urlObject The original URL.
+ * @param {Array<RegExp>} ignoreURLParametersMatching RegExps to test against
+ * each search parameter name. Matches mean that the search parameter should be
+ * ignored.
+ * @return {URL} The URL with any ignored search parameters removed.
+ *
+ * @private
+ * @memberof workbox-precaching
+ */
+export declare function removeIgnoredSearchParams(urlObject: URL, ignoreURLParametersMatching?: RegExp[]): URL;