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-window/utils/urlsMatch.d.ts

@@ -0,0 +1,11 @@
+import '../_version.js';
+/**
+ * Returns true if two URLs have the same `.href` property. The URLS can be
+ * relative, and if they are the current location href is used to resolve URLs.
+ *
+ * @private
+ * @param {string} url1
+ * @param {string} url2
+ * @return {boolean}
+ */
+export declare function urlsMatch(url1: string, url2: string): boolean;