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-recipes/googleFontsCache.d.ts

@@ -0,0 +1,18 @@
+import './_version.js';
+export interface GoogleFontCacheOptions {
+    cachePrefix?: string;
+    maxAgeSeconds?: number;
+    maxEntries?: number;
+}
+/**
+ * An implementation of the [Google fonts]{@link https://developers.google.com/web/tools/workbox/guides/common-recipes#google_fonts} caching recipe
+ *
+ * @memberof workbox-recipes
+ *
+ * @param {Object} [options]
+ * @param {string} [options.cachePrefix] Cache prefix for caching stylesheets and webfonts. Defaults to google-fonts
+ * @param {number} [options.maxAgeSeconds] Maximum age, in seconds, that font entries will be cached for. Defaults to 1 year
+ * @param {number} [options.maxEntries] Maximum number of fonts that will be cached. Defaults to 30
+ */
+declare function googleFontsCache(options?: GoogleFontCacheOptions): void;
+export { googleFontsCache };